473 



LITHOPHAGID^E. 



LITHORNIS. 



474 



Unguliita trantrerta. 



Saxicava. Animal elongated, eubcylindrical, having the mantle 

 closed on all sides, prolonged backwards by a long tube, double inter- 

 nally, a little divided at ita summit, and pierced inferiorly and ante- 

 riorly by a rounded orifice for the passage of a small, elongated, 

 delicate, and pointed foot ; mouth moderate, labial appendages small ; 

 branchial lamina; for the most part free, and very unequal on the 

 .-ame side. 



Shell thick, solid, covered with an epidermis, elongated, rounded in 

 front, truncated as it were posteriorly, gaping, irregular, equivalve, 

 very inequilateral, the posterior side being much longer than the 

 anterior ; umbones not very distinct ; hinge without teeth or with two 

 separated tuberosities more or leas developed ; ligament external ; 

 muscular impressions rounded and a little approximated, united by a 

 small straight pallial impression, very narrow, and occupying the 

 middle of the vnlve. (Rang.) 



M. De Blainville and M. Rang place the genus among the Pylorideans. 

 The former is of opinion that it differs little from Glycimeris. 

 . Mr. O. B. Sowerby ('Genera,' No. xxv.) includes in the genus Saxicava 

 sheila which, he observes, have had, in conformity with the various 

 views of authors, at least six different generic names. He apologises 

 for the conclusion to which he has coine in contradiction to so many 

 great authors, but gives the following reasons for his opinion. He 

 premises that it will not be disputed that Solen mimUus of Chem- 

 nitz and Montagu, Hiatella arctica of Daudin, Cardita arclica of 

 Bruguiere, and the Byssomya of Cuvier, are one and the same species ; 

 and that Leach's PhoUobiut includes as distinct species of the same 

 genus the Solen minutus of Montagu and the Mytilui rugosus of 

 Linnaeus. " Now the former of these," continues Mr. Sowerby, " is 

 Ifialclla arclica of Lamarck and Turton, and the latter Saxicava 

 rugota 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 propose 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 regular in shape and 

 more strongly spinose than the older, and are to all intents and pur- 

 pOMg Hiatella arctica, or Solen minutiu ; and the older specimens, 

 losing the strongly-marked double rows of spines, though always 



retaining indications 'of them, arid assuming a much less regular form, 

 become characteristic 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 : 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 Lamarckiau genera Iliatella and Sa.ricava, and his 

 Solen ininutua, merge into one : to show that the shells described as 

 distinct species under either of these generic names are identical is 

 not important to the present work ; it is therefore sufficient to observe, 

 that in all irregular shells that are either found 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 Myttius prcecisus and several 

 of the Saxicavcc described by Lamarck and Turton to be merely varia- 

 tions of S. rugosa, than which there is perhaps no shell more subject 

 to variety of form." To illustrate this exposition Mr. G. B. Sowerby 

 gives in his ' Genera' the following figures of Saxicava rugosa in dif- 

 ferent stages of ita existence. 



Saxicava rugosa. 



1, the young shell ; 2, inside, showing the teeth ; 3, a full-grown specimen 

 of the same ; 4, the inside, showing the muscular impressions. 



The distribution of the species is very extensive. The Northern 

 Ocean, the Britannic seas, the Mediterranean, the South Seas, Austral- 

 asia, and the warmer coasts of America, are recorded as localities. 



Mr. G. B. Sowerby remarks that the Saxicavis are frequently 

 found upon the outside of oysters, protected by their irregularities, 

 and in the clefts of rocks or corals, roots of sea-weeds, and perforating 

 oysters, chalk, limestone, and hardened clay. Those, he adds, which 

 themselves perforate the hollows in which they live are more regular 

 than others. 



Mr. Garner states that the crypts of Saxicava are not circular : 

 hence M. De Bellerue and Mr. Osier, in this instance, believe them to 

 be formed by the phosphoric acid secreted by the animal, and they 

 suppose this animal to inhabit those rocks only which are composed of 

 carbonate of lime, which last supposition Mr. Garner declares to be 

 not correct from his own knowledge. 



Mr. G. B. Sowerby observes that the species of this genus are not 

 numerous, and that they are not easily distinguished from each other, 

 as the reader may imagine from the confusion which has prevailed on 

 this subject. Lamarck recorded five species. Of the first two of 

 these (S. rugosa and S. Qallicana), one, according to M. Deshayes, 

 must be suppressed, being in reality only a variety of the other. S. 

 Australia and S. veneriformis, Lamarck's fourth and fifth species, 

 are identical, as we have already seen. To these M. Deshayes adds 

 S. Guerini, from tho Mediterranean, and S. rhomloides (?) as recent 

 species. Mr. G. B. Sowerby (' Zool. Proc.,' 1834) has added three 

 recent species collected and brought home by Mr. Cuming. 



Fossil Soxicavce. M. Deshayes, in his ' Tables,' gives the number of 

 fossil species as 11, all from the tertiary. He notes two species, S. 

 minuta and S. Pholadit, as both living and fossil (tertiary). 



For, the species of Pliolai and Lithodomus, see MYTiLiDiE and 

 PHOLADID,E. 



LITHOPHYTA. [POLYMFERA.] 



LITHORNIS, a genus of extinct Fossil Birds, described by Professor 

 Owen in the 6th volume of the ' Geological Transactions.' The most 

 conclusive evidence of the existence of birds at the period of the 



