Lamarck's Genera of Shells. 2§f? 



Shell somewhat concave, on the under side thin, and slightly 

 transparent ; disc divided by radiating striee. 



Indian Ocean, and common at the Isle of France. 2 Species. 

 PI. VII. Fig. 114. 



4th Family. 

 Calyptraciana. (7 Genera.) 



Branchias placed in a cavity on the back, near the neck, and. 

 projecting either in the cavity itself, or beyond it. The animals 

 breathe only water. 



Shell always external, covering. 



The animals of this family, in respect of form and position of 

 their shell, are nearly allied to the phyllidiana, especially the 

 patellse ; but the situation of their branchiae, in an insulated, 

 cavity on the back near the neck, sufficiently distinguishes them 

 from the individuals of that family, and requires that they should 

 be placed in a separate group. None of the shells belonging 

 to the Calyptraciana are operculated, wherefore the navicella 

 is decidedly excluded from this family. The seventh genus, 

 ancylus, is placed in it for the present, till the organization of its 

 animal inhabitant shall be more fully known. 



1. Parmophorus *. 



Body crawling, very thick, oblong-oval, rather widest at the 

 posterior end, obtuse at the extremities ; mantle, cleft in front, 

 falling vertically over the body, and covered by a scutiform shell. 

 Head distinct, situated under the cleft of the mantle, with two 

 conical, contractile tentacula, with two eyes at their external 

 base. Mouth below, hid in an obliquely truncated funnel. 

 Branchial cavity opening anteriorly, but behind the head by a 

 transverse fissure, and containing two lamellar, pectinate, pro- 

 jecting branchiae. Orifice of the anus in the branchial cavity. 



Shell oblong, subparallelopipedal, rather convex above, 

 retuse at the extremities, anteriorly emarginate, sinus slight, 

 apex small, inclining to the posterior side. Lower surface 

 slightly concave. 



Type. ParmopJioriis australis t. 



• From ma^ixi, a shield, and ifi^oi, to bear. 

 t Hiuthem, 



