CAPULUS. HIPPONYX. CREPIDULA. 



matter these animals yield is so small, it is difficult to explain 

 how they could furnish so active a trade; and it must have been 

 that the ancients used for the same purposes the purple liquid 

 secreted by larger and more common mollusks, such as the 

 aplysia, which we have yet to mention. 



20. The FAMILY OF PECTINIBRANCH CAPULOIDES is recog- 

 nised by the shell being widely open, slightly turbinated, and 

 without either notch, syphon, or operculum. The conformation 

 of the animal differs but little from that of other mollusks of the 

 same order ; there is only a single branchia, often with very long 

 filaments, attached transversely to the arch of the respiratory 

 cavity. 



In this division are arranged the genera of Pileopsis, Hippo- 

 nyx, Crepidula, Calyptraa, Sigaretus, fyc. 



21. Animals of the genus Pileopsis^ or Capulus 

 (fig. 71), have their branchiae on the anterior edge 

 of the respiratory cavity ; the shell is conical, and 

 presents at its summit the commencement of a spire; 

 their neck is covered by a membranous plaited veil, 

 and they have two conical tentacles, and a tolerably 

 long trunk or proboscis. They inhabit the sea- 

 shores of warm countries. 



22. The genus of 

 Hipponyx (fig. 72) con- 

 sists of fossil shells, 



which closely resemble the preceding, 



but are very remarkable for a support 



formed by calcareous layers, upon 



which they rest, and which seem to 



have been secreted by the foot of the 72 ._ H ippoNvx. 



animal. 



23. The CrepidulcB have an oval 

 shell, the whole base of which is 

 half closed by a horizontal plate, 

 which supports the abdominal sac 

 above it, and is covered beneath by 

 the foot (fig. 73). 



Fig. 73. CREPIDULA. 



20. How is the family of Pectinibranoh Capuloi'des distinguished t 

 (Capuloides, from the Latin, capulus, a hilt or handle, and the Greek, eidos, 

 resemblance.) 



21. What are the characters of the genus Ca'pulus? (Capulus. Latin, a 

 hilt.) 



22. What are the characters of the genus Hippony'x? (Hipponyx, from 

 thr- Greek, ippos, a horse, and onux, nail ; horse nail, or hoof.) 



23. What are the characters of the genus Crepi'dula ? (Crepidula. Latin, 

 a slipper.) 



