ORDER P ECTINIBRANCHIATA. COMB-GILLS. 



135 



THE BUCCINOID TRIBE. 



CERITHIUM. Shell turreted ; aperture short, oblong, oblique, terminated 

 at the base by a short truncated or curved canal ; never notched ; a slight 

 channel at the upper extremity of the right lip ; operculum small, orbicular, 

 horny. 



The spire of the shell constitutes at least two-thirds of the whole length ; 

 the shell has the form of an elongated pyramidal cone, the surface is in 

 most species striated or tubercular, and in some varicose. 



The animals of this genus walk on a small roundish disc or foot. The 

 head is truncated below, and edged with a crest or fringed border ; the 

 tentacute are two in number, acute, and at the outer part of the base, have 

 a small enlargement bearing the eyes. The type of the genus is C.palustre 

 (Slioiribus pal'ustris, Lin.). Lamarck enumerates thirty-six recent and sixty 

 fossil species. 



Illustrations : Ceritluum Lamarckii, C. fuscatum, C. telescopium (oper- 

 cule of). 



THE CAPULOID TRIBE. 



ILLUSTRATIVE EXAMPLES. 



PLATE 7. 



CAPULA. See PILEOPSIS. 



PILEOPSIS. Shell exterior, obliquely conical, bent forward, with the 

 summit nearly spiral ; aperture rounded, elliptical, with the anterior margin 

 shortest, the posterior larger and rounded ; under the hinder edge is an 

 elongate, bent, transverse, muscular impression. Animal with two conical 

 tentacula, the eyes at the base ; branchiae disposed in a row beneath the 

 anterior margin. 



Type of the genus, Patella vel Capuim Hungarica, Linnaaus. The animals 

 of this genus are generally found on rocks, and shells in rather deep water ; 

 three species are indigenous, and a fourth is found in a fossil state. 



The genus Pileopsis is sometimes called Capvdus. 



Illustrations : Capulus Hungarians, Pileopsis mitrida, P. cremdata. 



HIPPONIX. Shell univalve, conical ; apex recurved, subspiral, sublateral ; 

 spiral cone very rapidly enlarging ; mouth irregular ; muscular impression 

 horse-shoe shaped, submarginal. Animal tentacula two, conical ; eyes at 

 their outer base ; foot small, transverse, folded across the upper surface ; 

 reflexed, and attached to marine bodies, which it often covers with a shelly 

 deposit. 



This genus of conical, somewhat spiral, univalve shells, was established 

 by Defranc, but since shown to be exactly synonymous with the genus 

 Capulus of De Montfort and Lamarck, belonging to the family Capulida;. 

 It has been very commonly referred to the Brachiopodes, to which it has 

 not the least resemblance, as has been proved by the dissection of the 

 animal, published by Blainville. 



The animal has the peculiar property of secreting a shelly plate, which 

 closes the base of the shell, so as to give the shell somewhat the appearance 

 of a bivalve, to which class some naturalists have been inclined to refer the 

 genus. 



The type of the genus is Patella Hungarica and Patella mitrata of 

 Linnsus ; Lamarck describes many fossil species from the Paris basin. 



Illustration : Hipponix cornucopias. 



CREPIDULA. Animal with the head forked anteriorly ; tentacula two, 

 conical, with the eyes at the outer side of their base ; mouth simple, 

 without maxilla, placed at the bifurcation of the head ; branchia solitary, 

 subpenicillate, projecting beyond the branchial cavity, on the right side of 

 the neck ; mantle never extending beyond the shell ; foot very small ; anus 

 lateral ; shell oval or oblong, convex externally, concave within ; spire much 

 inclined towards the margin ; aperture partly closed by a horizontal lamina. 

 I Separated from the genus Patella of Linnams. The shell not only covers, 



but partly unsheathes the animal, by means of the lamina which partly 

 closes the mouth. It is not operculated. 



Illustrations: Crepidula porcellana, C. Peruviana, C. unguis, Dispotea 

 Bironensis. 



CALYPTILEA. Shell conoid, orbicular at the base ; vertex central, sub- 

 acute, imperforate ; cavity furnished with a convoluted lip, or spiral septum. 



This genus of univalve shells was separated from the Patella of Linnaeus. 



Patella G'hinensis, which is a British species, is a good example of this 

 genus. 



Illustration : Calyptera Neptuna. 



SIPHONARIA. Shell patelliform. elliptical, ribbed ; apex nearly central, 

 well marked, obliquely inclining towards the posterior margin; muscular 

 impression of a horse-shoe partly encircling the central disc but interrupted 

 in front ; a canal or siphon on the right side passing from the apex to the 

 margin, and which divides the right lobe into two. Animal oval, depressed ; 

 head two lobes ; tentacles wanting ; a narrow veil on the head ; mantle 

 crenulated on the borders ; branchia? situated between the foot and the 

 mantle in the form of a square membrane. The hood of the animal is 

 described by Quoy and Gaimard as being of considerable size, which is 

 rounded and furnished above with sessile eyes; it emits at pleasure a 

 viscous secretion of a white colour ; it has two salivary glands which open 

 into the oesophagus, and its liver has four lobes. The siphon, which some 

 of the species possess, distinguishes Siphonaria from Patella. 



Illustrations : Siphonaria radiata, S. gigas, Gadinia qfra. 



SIGARETUS. Shell somewhat ear-shaped, patulous, almost orbicular, the 

 left margin short, spiral ; aperture anterior, very wide, longer than broad, 

 the margins united ; mantle enveloping the shell, its anterior sinistral 

 margin notched at the branchial opening; tentacula two; eyes at their 

 outer base. 



Type of the genus, Bulla haloitidea ; Montagu. Two species, both of 

 which are found on the coasts of Britain, though not very commonly. 



Illustration : Sigaretus haliotideus. 



CORIOCELLA. Distinguished from Sigaretus by a horny and membrauous- 

 like shell ; in all other respects similar. 



Illustration : Coriocella nigra. 



The PTEROPODOUS SUB-CLASS consists of but few animals, remarkable for 

 the wing-like expansions placed on each side of the narrow neck, which 

 connects the head with the visceral bag: these 

 organs, in Hyalea and Pneumoderma, are doubtless 

 the locomotive organs, for in the latter a pair of 

 distinct branching gills exist externally on the 

 caudal extremity of the body ; and in the former 

 the gills are situated on each side of the body in a 

 cleft of the visceral bag. But in Clio, the wings 

 serve both as locomotive and branchial organs, 

 presenting, under the microscope, as Cuvier ob- 

 serves, a very delicate, close, and regular vascular 

 network, connected with the internal vessels and 

 the heart ; neither is there any other organ which 

 has any resemblance to gills. Some genera, as Hyalea and Cleodora, con- 

 tain shells in the walls of their visceral bag, which others, as Clio, have not. 



Hyalea. 



SUB-CLASS ACEPHALA. HEADLESS. 



ACEPHALS. This remarkable class of Molluscous Animals is distin- 

 guished by the absence of any head, and by the toothless mouth being 

 almost always concealed within the folds of the mantle, which in different 

 form encloses the animal, and is itself enveloped by an external covering, 

 in one Order gelatinous or coriaceous, and in the others testaceous or shelly. 

 Their food consists generally of minute animals, which are brought to their 

 mouths by the currents in the surrounding water, excited by the motions of 

 the mantle. All the class are aquatic ; and upon the different form and 

 disposition of their branchiae or gills, their distribution, by Blainville, into 

 Orders depends. 



1 . The Heterobranchiate Order : 



These are the TU.VICATA of Lamarck (so distinguished on Plate 8), who 

 places them between his RADIATA and VERMES ; but admits that by one 



