Saxicava.] 



MUSEUM OF ANIMATED NATURE. 



279 



more or less truncated. The hins;e presents two 

 slender teeth in one valve, and three in the other. 



The mantle of the mollusk I'orms two rather long 

 posterior siphons with radiated orifices. 



The mollusks which compose this genus are litho- 

 phasifous, and excavate galleries in stones and 

 madrepores ; these galleries are more or less pro- 

 portioned to the size and form of the shells, and in 

 these they live : they are without an epidermis, and 

 their colour is generally of a dirty white. 



Mr. G. B. Sowerby, who is disinclined to admit 

 of any marked distinction between Venus (or the 

 subgenus Pallastra) and Venerupis, says, " It is well 

 known that Venus perforans of Montfort (Venerupis 

 peiforans, Lam.), and some of its congeners, live in 

 cavities perforated in chalk and limestone rocks ; 

 and that Venus Pallastra, and V. decussata, and 

 several other species that resemble them in form 

 and appearance, are found buried in the sand : an 

 apparently well marked difference therefore exists 

 in the habits of their respective animals. ■ 



We think, however, that we have evidence to 

 prove that there exists in reality very little dif- 

 ference, and that the cavities in which Lamarck's 

 Venerupes live are rather the natural consequence 

 of the action of the sea-water, in conjunction with 

 some of the excretions of the animal upon the chalk 

 or limestone, than of any power of the animals 

 themselves to pierce independently of such action ; 

 so that the difference is really only in the nature 

 of the shore on which the very joung shells are 

 accidentally deposited, those which are thrown upon 

 a sandy bottom burying themselves in the sand, and 

 such as are deposited upon limestone or chalk pro- 

 ducing a cavity in which they live." Mr. Sowerby 

 then proposes to unite under one genus the Vene- 

 rupes of Lamarck, and several species of Venus, as 

 V. textile, V, Pallastra, &c. ; for which genus he 

 proposes the name of Pallastra, rejecting altogether 

 that of Venerupis. We have already adverted to 

 two species of Venus, which are assigned to Pallas- 

 tra, and noticed the views of Deshayes respecting 

 the genus. 



M\L de Blainville and Rang restrict the genus 

 Venerupis to the rock-boring species. 



Its range is very extensive ; many species occur 

 on the shores of Europe and in the South Seas. 



2978. — The Boring Rock-Vexus 



(Venerupis perforans). This species is found on 

 the coast of England and the adjacent continent. 

 It is subject to some variety, a represents the shell 

 tVom a figure by Montagu ; b, the shell from nature. 

 About eight species are known living and six 

 fossil. 



We now ti#fi to Petricola, into which Mr. G. B. 

 Sowerby merges the genus Ruppellaria. 



Though Mr. Sowerby is inclined to bring the 

 genus Petricola close to the Pholadariae, yet it must 

 be confessed that the animals differ but little from 

 those of Venerupes, to which they approximate also 

 in the form of the shells ; indeed M. I'eshayes 

 remarks that hereafter we shall probably be obliged 

 to unite Petricola and Venerupis, which in reality 

 exhibit but trifling distinctions ; and this resem- 

 blance exists not only in the shells, but also in the 

 inhabiting mollusks. 



Mr. Garner, in his anatomical classification of 

 the Lamellibranchiata, makes no mention of Pe- ; 

 tricola, which he probably regards as identical 

 with Venerupis, to which he devotes a considerable 

 ipace. 



The Petricolae are widely spread, and are rather 

 numerous on the coast of the warmer regions of 

 America : they live in cavities of the rock formed 

 by their own agency, and which are adapted to the 

 (hape of the shell itself, proving that in the work 

 of boring the rock there is no rotatory motion. 



The specie* vary considerably in the degree to 

 ■ihich the shell is lengthenod posteriorly. Figs. 2979 

 and 2980, Petricola pholadiformis ; Fig! 2981, 

 Petricola dactj his ; Fig. 2982, Petricola ochroleuca ; 

 Fig. 2983, Petricola rupestriii ; Fig. 2984, Petricola 

 subglobosa. 



Eleven recent species of this genus are recorded 

 by Lamarck and Deshayes, to which must be added 

 ten new species, from the western coast of South 

 America and the islands of the South Pacific, de- 

 scribed by Mr. G. B. Sowerby, in the ' Proceeds. 

 Zool. Soc." 1839, pp. 46, 47. Many were found in 

 hardened clay and mud at low-water, some in stones, 

 and one in mother-of-pearl shells. 



Several fossil species are recorded, some from 

 ^frata below the chalk, others in tertiary deposits. 



M. de Blainville took from the genus Cypricardia 

 (if Lamarck some species which he regarded as 

 approximating to Venus, and formed them into ! 

 a genus, to which he gave the name of Corallio- 

 phaga. 



The shell is oval, elongated, and finely radiated 

 from the summit to the base ; the form is cylin- 

 drical and equivalve. The hinge presents two 

 small cardinal teeth, one of which is slightly bifid, 



ll 



in front of a sort of lamellar tooth, under a weak 

 external ligament. Pallial impression iiexuous 

 posteriorly. 



The mollusk is not known, but most probably has 

 elongated siphons. 



2985. — The Cardite Coralliophaga 



(Coralliopliaga carditoidea). Cypricardia coraliio- 

 phaga, Lamarck ; Cardita coralliophaga, Brug. ; 

 Chama coralliophaga, Gmel. 



This species is found often in abundance in 

 the masses of madrepore and other corals at St. 

 Domingo and the Antilles. We may here observe 

 that M. Deshayes refers these shells to the genus 

 Crassina. 



The next genus, Clotho, exists only in a fossil 

 state, no recent living species being known. 



The shell is oval, equivalve, and lonafitudinally 

 striated ; the hinge presents a bifid tooth curved 

 back into a hook-like form, rather longer in one 

 valve than the other. 



2986.— Faujas's Clotho 



{Clotho Faujasii). This species, the only one re- 

 corded, was detected by Faujas in the fossil shells 

 of certain species of Cypricardia, which were found 

 imbedded in the stone which, when alive, they had 

 eroded. The upper figures represent the shell of 

 the natural size ; the lower figures (a) represent it 

 magnified. 



We may now advert to the genus Ungulina, first 

 established by Daudin, and adopted by Lamarck. 



The animal is unknown. The shell is described 

 by M. Rang as loneitudinal, or transverse, irresrular, 

 not gaping, equivalve, subequilateral ; the umbones 

 tolerably developed and eroded. The hinge pre- 

 sents a cardinal tooth in each valve, short and sub- 

 bifid, and an oblong marginal furrow or depression 

 divided into two parts by a contraction : the liga- 

 ment is subinternal, and inserts itself in these fiir- 

 rows. The muscular impressions are elongated ; the 

 pallial mark is simple, not flexuous. 



2987. — The Transverse Ungulina 



(Ungulina transversa). M. Deshayes, in his re- 

 marks on the present genus, considers it to be nearly 

 allied to Lucina, and states that the ligament of the^ 

 hinge is not internal, but really external ; and, more-' 

 over, that the two species described by Lamarck are 

 mere varieties of one. 



The Transverse Ungulina is stated in the last 

 edition of Lamarck to be a native of the seas of 

 Senegal ; and we learn that Mr. G. B. Sowerby has 

 received specimens from Senegal, and has good 

 reason to believe the shells to be marine. 



From observations recently made by M. Rang, 

 there is reason to believe the ungulina to be rock- 

 boring in its habits. This is inferred from certain 

 fossil shells belonsing to the genus found in the 

 environs of Bordeaux. 



The right hand figure below represents the cha- 

 racters of the hinge enlarged. 



We now come to the genus Saxicava. 

 This genus is placed by M. de Blainville and M. 

 Rang among the Myadae (the Pylorideans of the 

 former), and they are very probably correct in their 

 views M. de Blainville indeed observes that Saxi- 

 cava differs but little from Glycimeris, Lam. 



Mr. G. B. Sowerby, who adopts the genus Saxi- 

 cava, refers to it various shells, which in conformity 

 with the views of different naturalists, have been 

 placed in six separate genera, nor has he done this 

 without tho most patient and rigorous scrutiny. 



In the first place, he says, it is beyond dispute, 

 that the Solen minutus of Chemnitz and Montagu, 

 the Hiatella arctica of Daudin, the Cardita arctica of 

 Brugui6re, and the Byssomya of Cuvier are one and 

 the same species ; and secondly, the Pholeobius of 

 Leach includes, as distinct species of the same 

 genus, the Solen minutus of Montagu and the My- 

 tilus rugosus of Linnaeus. 



Here then are six generic titles, Solen, Hiatella, 

 Cardita, Byssomya, Pholeobius, and Mytilus, under 

 which have been described shells which he regards 

 as Saxicavae. 



Now, says Mr. Sowerby, the Solen minutus of 

 Montagu "is the Hiatella arctica of Lamarck and 

 Turton, and the Mytilus rugosus, Linn., is the Saxi- 

 cava rugosa of the same authors. Thus all the six 

 genera are reduced to one by Dr. Leach, whose 

 authority is indisputably very great in such matters. 

 We do not however (continues Mr. Sowerby ) pro- 

 pose to our readers to take it as conclusive, but will 

 state that we possess, as Dr. Leach did, a series of 

 specimens, the young ones of which are more regu- 

 lar in shape and more strongly spinous than the 

 older, and are to all intents and purposes Hiatella 

 arctica or Solen minutus ; while the older specimens, 

 losing the strongly marked double row of spines, 

 though always retaining indications of them, and 

 assuming a much less regular form, become cha- 

 racteristic specimens of Saxicava rugosa. The 



hinge-teeth of the younger specimens may be 

 advanced as an argument against the identity of 

 these shells ; it is however well known that in many 

 shells, particularly those that are irregular, the 

 teeth become obsolete with age : and thus if the 

 hinge-teeth, the general form of the shells, or the 

 double row of spines cannot be depended upon as 

 generic distinctions, the Lamaickian genera Hia- 

 tella and Saxicava, and Lamarck's Solen minutus, 

 merge into one." " It is," he adds, " sufficient to 

 observe, that in all irregular shells which are found 

 either attached to or imbedded in rocks, corals, roots 

 of sea-weeds, &c., the general form cannot be taken 

 as a character, and we believe the Mytilus piaecisus,. 

 and several of the Saxicavae described by Lamarck 

 and Turton, to be mere variations of Saxicava. 

 rugosa, than which there is no shell, perhaps, more 

 subject to variety of form." (' Genera,' No. xxv.)< 

 Mr. Sowerby illustrates his views by the figures of 

 Saxicava rugosa in different stages df existence. 



2988.— The Rijggse Saxicava 



(Saxicava rugosa'). A, the young shell, with ifg- 

 double row of spines ; B, the inside of the valves, 

 showing the teeth ; C, C, full-grown specimens,' 

 showing the difference in the fifjure of the valves • 

 p, the inside of the valves, showing the muscular- 

 impressions. 



The views of M. Deshayes coincide very nearly 

 with those of Mr. G. B. Sowerby. When, says M. 

 Deshayes, " we examine the shells of Byssomya, and 

 compare them with those of Saxicava, we find no dif- 

 ference between them ; whilst in the animals a much 

 greater discrepancy exists, because the Byssomyse 

 perforate, and carry behind a rudimentary foot a 

 byssus, like that of the Mytili. The mantle is 

 closed for a good part of its length, and is prolonged 

 backwards into two siphons, joined together to the 

 summit. If we appreciate these differences at their 

 just value, we may easily perceive that they are not 

 of such great importance as they may appear to be, 

 for a byssus affords the means of living on one and 

 the same spot, no less than it secures the faculty 

 of penetrating stones ; we must therefore consider 

 the character of the byssus in the Byssomyae as of 

 little value, for the greater number of zoologists 

 have united this genus to the Saxicavoe." With 

 respect to Solen minutus and Hiatella arctica, he adds, 

 they are the same ; and that the species belongs to- 

 the byssiferous Saxicavsje, as he has proved by an 

 examination of the animal. 



M. Rang thus details the generic characters of 

 Saxicava, as presented by S. rugosa : — 



The shell is thick, solid, and covered with an 

 epidermis ; it is of an elongated form, rounded in 

 front, more or less truncated posteriorly, gaping,, 

 and irregular. The umbones are not very distinct ; 

 the hinge is without teeth, or presents tvi-o separated 

 tuberosities more or less developed ; the ligament is 

 external. The muscular impressions are "rounded, 

 and united by a small straight pallial mark, which 

 is very narrow, and runs along the middle of the valve. 

 The mollusk has the mantle closed, with an an- 

 terior orifice for the passage of an elongated delicate- 

 pointed foot, and with two posterior siphons united, 

 together, forming a double tube. 



The range of the Saxicavae is very extensive ; 

 they are found in the Northern Ocean, the British 

 seas, the Mediterranean, the seas along the warmer 

 parts of America, the South seas, &c. Some are 

 found in the interstices between agglutinated oysters, 

 and in the fissures of rocks or corals ; others bore 

 under the roots of sea-weeds, or perforate chalk, 

 limestone, and hardened clay ; and Mr. Sowerby 

 states that those which the'mselves perforate the 

 hollows in which they live have a more regular 

 form than the others. 



The species of this genus, as may be supposed 

 from the variations to which they are subject (and 

 which have already led to no little confusion), are 

 not easily to be distinguished from each other. 



The species however are not numerous ; M. Des- 

 hayes gives the number of recent species as five, 

 to which must be added three described by Mr. G. 

 B. Sowerby in the ' Proceeds. Zool. Soc' 1834, p. 

 88. They were collected by Mr. Cuming, and were 

 respectively found in masses of coral, in sandy mud, 

 and the clefts of rocks. About twelve fossil species 

 are known. 



2989. — The Northern Saxicava 



(Saxicava Pholudis). Mytilus Pholadis. iMiill. ; 

 Mya byssifera, Fabr. ; Byssomya Pholadis, Cuv. 



As we have already said, Mr. G. B. Sowerby refers 

 Cuvier's Byssomya to Saxicava. 



This species (if it be distinct from S. ruffosa) 

 inhabits the nortliern seas, living in the fissures of 

 rocks, and attached by its by.ssus ; scjmetimes how- 

 ever it lodges in stones or buries itself in the sandy 

 mud at the roots of sea-weeds ; in the latter in- 

 stances, according to Fabricius, the byssus becomes 

 lost. 



