FAMILY |]. FISSURACEA. 17 
Family 1. FISSURACEA. 
Testa patelleformis, animal sepissimé obumbrans, aut perforata, aut 
emarginata, aut impressione siphonali interné imbuta. 
This family, which we have ventured to introduce under the above new 
title, includes that portion of the Cervicobranchiate Gasteropoda whose 
shell exhibits the channel by which the water is communicated to the 
branchial cavity, either by an internal siphonal impression, by a marginal 
sinus, or by a complete perforation or fissure. They were included by 
Lamarck with ‘‘ Les Calyptraciens,” but the necessity of dividing that 
family has been successfully determined both by De Blainville and Gray ; 
by the former they are assigned to different orders; by the latter, to 
different sections of the same order. The distinguishing character of the 
Fissuracea, namely, the perforation, fissure, or siphonal impression, is 
certainly indistinct, if at all visible, in the shell of Lottia; but as the 
structure and arrangement of the breathing apparatus is known to be 
the same, we have regarded the Lottie as being intermediate between 
the Patelle and the Siphonarie. 
The family of the Fissuracea includes the five following genera: 
Loria. EMARGINULA. 
SIPHONARIA. FISSURELLA. 
PaRMOPHORUS. 
LOTTIA, Gray. 
Testa patelleformis, regularis, plerumque depressiuscula, vertice antico, 
prope ad marginem incumbente, nonnunquam feré marginali. Im- 
VOL. II. LL 
