MR. B. GARNER ON THE SHELL-BEARING MOLLUSCA. 39 



canal to attain the right flank. In Sepia the branchisB are again 

 symmetrical and abdominal. 



The shell of the young Sepia is composed of distant plates, only 

 connected by minute transversely striated laminae or flattened 

 tubes, producing by their insertion a beautiful appearance of 

 sinuous lines, very like those of a Baculite or Ammonite ; and the 

 spongy part of the shell, so constituted, is probably filled with air 

 from the cavity of the body situated immediately in front, the 

 intervening membrane having a peculiar structure. This cavity of 

 the body exists in much lower moUusks ; air being apparently 

 secreted in it, to lighten the animal. 



The author thinks that, in considering the anatomy and form of 

 the body of the Grasteropoda, about ten species may be taken as 

 types of corresponding families. 



1. Patella and its congeners. — He claims to have been one of 

 the first to show the termination of the oviducts and renal organs 

 between the processes of the branchiae in the Chitons. As they 

 are commonly phytivorous, the intestine is often very long and 

 disposed in large coils, in double apposition ; the buccal apparatus is 

 very remarkable. Chitonellus diflers but slightly from Chiton, the 

 central elements of its tongue, however, being little developed, 

 though having the same tessellated basement membrane. The 

 tongue of Emarginula differs much from that of Patella, having 

 an immense number of serrated side-hooks and a dilated middle 

 portion. 



2. CaltptrjEA, Sfc. — The moUusks of this division have often 

 suprannchal branchiae, as have some of the last ; the sexes also 

 are frequently separate, rendering copulation necessary ; and they 

 are sometimes partially spiral, with a tendency to form an oper- 

 culum. However, the little Ancylus fluviatilis appears to be what 

 is commonly called hermaphrodite, with a branchial lamina on 

 the left side, together with the heart and openings of the genital 

 organs ; the stomach has a caecum, and the penis a long filiform 

 appendage ; the female parts opening near the rectum and behind 

 the male organs. It must respire by water rather than by air, 

 for, in a rapid stream, the stones at the bottom are covered with 

 Ancyli (upon which also its round oothecae, each containing four 

 or five ova, are deposited), and it appears impossible for them to 

 get to the surface to breathe. On the contrary, the \2k.e- Ancylus, 

 though the margin of its mantle is ciliated, may perhaps come to 

 the surface, ascending the stalks of the "Water Persicaria, on 

 which it is mostly found, and on which its oothecae are deposited. 

 When the dark cuticle of this last minute creature is removed, 



