CHAP. IX. TECTIBRANCHIA. 249 



essential differences. Lamarck has judiciously sepa- 

 rated these into two groups^ to the first only of which 

 he retains the old name of Bulla : some of these may, 

 possibly, be connected to the aberrant Volutidce ; while 

 others, by uniting with Akera, will open a passage to 

 the Cephalapoda by means of Gasteropteron. At all 

 events, the situation of the Tectibranchia is clearly 

 intermediate between the Gasteropoda and the Ce- 

 phalopoda. 



(233.) The Phyllidin^e, as Lamarck has already 

 shown, evidently connects the Cyclohranchia to the 

 Aplysia, or sea-hares ; hence its general form is that of 

 a Chiton, being oblong oval, but without any testaceous 

 covering. The mantle does not appear divided, but 

 covers the back like a shell, and is usually of a strong 

 coriaceous substance : there are two small tentacula, 

 shaped as in Doris, on the upper surface ; and two 

 others, still smaller, beneath, on the sides of the mouth, 

 which Cuvier says " is a small proboscis ; " but this 

 does not appear in Riippell's figure of P. pustulosa * , 

 which was taken from the life. The branchia are in the 

 form of two long leaves or pectinated processes, placed 

 on each side of the body, under the edge of the mantle, 

 for its whole length. The anus is on the hind part, 

 and the genital orifice forward, under the right side. 

 In the sub-genus Diphyllidea, the branchia are the 

 same; but the anterior part is more narrowed, and the 

 second pair of tentacula are reduced to tubercles. 

 These animals are not numerous, and are almost con- 

 fined to the Eastern Ocean. 



(234.) In Aplysia t, the typical characters already 

 mentioned begin to appear. These animals have the 

 appearance of a neck. The upper tentacula are shaped 

 exactly like those of a hare, whence the common name 

 of SeaJiares, given to these animals in most countries 



* Ruppell, Atlas i. pi. 11. fig. 1. 



f A very costly work by M. Sander Rang and De F^russac on this group 

 has been published ; but, as it is out of the reach of ordinary naturalists, we 

 do not possess it, and therefore cannot consult it. This is one out of the 

 numerous evils of these ouvrages de Ittxe. 



