MOLLUSCA. 789 



Sexes distinct. Tongue long, linear, mostly beset densely with 

 teeth and barbs. Shell resembling a shield, dorsal, not turbinated, 

 with aperture ample. 



The position of the branchiae brings this family into the neigh- 

 bourhood of the ffypobranchiata, and thus LAMARCK refers Patella 

 and Chiton with Phyllidia to the same family. In other respects, 

 however, there exists much difference amongst these animals, as at 

 once appears from the disposition of the sexual organs, since in 

 this division the sexes are distinct. Still, in a natural sequence of 

 the animal kingdom, the Cyclobranchiata ought to form as it were 

 the transition of the Ctenobranchiata to the three preceding families, 

 the Opisthobranchiata of MILNE EDWARDS. 



That some individuals of Patella are female, others male, was observed 

 by GEAT (Annals of Nat. Hist. i. p. 482), by MILNE EDWARDS (Annales 

 des Sc. nat., 2e S^rie, xin. p. 376), by PETERS and ROBIN (MUELLER'S 

 Archiv, 1846, s. 134) and by WAGNER (besides in Patella) also in Chiton 

 (Annals of Nat. Hist. VI. p. 70). 



Chiton L. Shell multivalve, made up of (eight) testaceous 

 scales arranged in a longitudinal row, incumbent on back. Mantle 

 at the circumference not covered by shell, with margins hard, 

 coriaceous, often aculeate or squamose. Ventral disc elongate, 

 narrower than body. Eyes and tentacles none ; head crested by 

 a wavy veil. 



With LINNAEUS there are three genera of Testacea multivalvia : 

 Chiton, Lepas and Pholas. The last genus belongs to the Conchifera 

 or Bivalvia ; Lepas is, as we stated above, a family of the Crustacea. 

 Thus there remains the genus Chiton alone as a true multivalve 

 mollusc. That it has no affinity or true similarity with the Cirri- 

 pedia (Lepas L.), to which BLAINVILLE united it under the name of 

 Malacoentoma, now requires no demonstration ; but many authors, 

 both of earlier and later periods, still maintain that it differs too 

 remarkably from the rest of the Gasteropods to allow it to remain 

 in the neighbourhood of Patella, and that it forms the transition to 

 the ringed worms (MiLNE EDWARDS Ann. des jSc. nat., 3e Se"rie, ix. 

 1848, p. 110). It appears to us that these writers attach too much 

 weight to the external resemblance of the pieces of shell to rings of 

 articulate animals. In the internal structure there is, perhaps, with 

 the exception of the remarkable occurrence of two oviducts (or vasa 

 deferential), and two sexual apertures placed at the side, nothing to 

 be met with that can indicate a remote affinity with the Articulate. 



