STRUCTURE OF THE TURBO PICA. 



43 



from the shape of the opening, resembling a human ear. Many 

 of these gasteropods are of considerable size. One species is 

 found on the shores of the Mediterranean. 



ORDER OF PECTZKIBRANCHIATA.'^ 



26. This division of the class of Gasteropods is the most 

 numerous in genera and species : it comprises nearly all the 

 mollusca, in which the shell is univalve and spirally twisted, 

 m vh h ah ov 



Fig. 32. — ANATOMY ov A PECTiNiBRANCH GASTEROPOD. Turho Pictt {See Jig. 44). 



Explanation of Fig. 32. — Anatomy of a pectinibranch gasteropod (the 

 Turho pica), to show the arrangement of the respiratory cavity : — p. the foot 

 of the animal ; — o. the operculum ; — t. the trunk ; — la. the 'tentacles ; — y. the 

 eyes ; — /n. the mantle, split open longitudinally so as to expose the respi- 

 ratory cavity : — -/. the anterior edge of the mantle, vi^hich in its natural po- 

 sition covers the back of the animal, and leaves there an opening or great 

 slit, through which the water reaches the branchiae ; — h. the branchiae : — vb. 

 the branchial vein which goes to the heart (c) ; — ah. the branchial artery ; — 

 a. the anus ; — i. the intestine ; — e. the stomach and liver ; — ov. the oviduct. 

 Above the nucha or nape, we see the cephalic (nervous) ganglion, and the 

 salivary glands ; — d. fringed membrane, which below borders the left side 

 of the opening of the respiratory cavity. 



* Pec'tinibranchia'ta. — From the Latin, peclen, a comb, and branchia^ 

 gills ; because the branchiae or gills {Jig. 32, b) resemble a comb in form. 



26. What are the peculiarities of the pectinibranch ga'steropods 

 what parts of the shell do we find the respiratory cavity ? 



In 



