GASTEROPODA PECTINIBRANCHIATA. 251 



FAMILY II. 



CAPULOIDA. 



RECENT researches have convinced us that it is to the Trochoida that we 

 must approximate this family, which contains five genera, four of which are 

 taken from the Patella?. They all have a widely opened, scarcely turbinated 

 shell, with neither operculum, emargination, nor syphon ; the animal resembles 

 the other Pectinibranchiata. There is but one branchial comb transversely 

 arranged on the roof of the cavity, and its filaments are frequently very long. 



PILEOPSIS, Lamarck. 



A conical shell with a recurved and spiral summit, which has long caused it 

 to be placed among the Patellae; the branchiae are in one range under the 

 anterior margin of the branchial cavity ; the proboscis is long, and there is a 

 closely plaited membranous veil under the neck; the eyes are at the external 

 base of the conical tentacula. The 



HIPPONYX, Defr. 



Would appear from the shell to be a fossil Pileopsis, very remarkable, however, 

 for a bed, formed of calcareous matter, on which it rests, and which probably 

 exuded from the foot of the animal. 



CREPIDULA, Lamarck. 



The shell oval, with an obtuse horizontal point, directed obliquely backwards 

 and laterally, the aperture forming the base of the shell, which is half closed 

 beneath and behind by a horizontal plate. The abdominal sac which contains 

 the viscera is on this plate, the foot beneath, and the head and branchia? forwards. 

 The latter consists of a range of long filaments attached under the anterior 

 margin of the branchial cavity. The eyes are at the external base of two conical 

 tentacula. The genus 



PILEOLUS, Sowerby, 



Appears to consist of Crepidulae in which the transverse plate occupies half the 

 aperture; their shell, however, is more like that of a Patella. They are only 

 found fossil. 



NAVICELLA, Lamarck. 



The shell resembles a Crepidula, except that the summit is symmetrical and 

 laid on the posterior margin, and that the horizontal plate is less salient. The 

 animal is also provided with an additional irregularly shaped testaceous 

 plate, horizontally connected with the superior surface of the muscular disk 

 of ils foot, and covered by the abdominal sac, which it partially supports. 



