GASTROPODA. 283 



nated ; adductor muscle horseshoe-shaped or oval ; jaws rudimentary. 

 Visceral mass spiral, lateral cervical lobes present, and there are acces- 

 sory genital glands. Radula. with a sub quadrangular central tooth, 

 the margin pectinated, the central cusp longer ; lateral teeth with 

 denticulate margins ; marginals narrow, curved, denticulate. 



Shell conic, patelliform, the summit more or less spiral ; interior 

 polished, porcellanous, chambered by a basal plate or variously shaped 

 process, supporting the viscera ; peristome entire. No operculum or 

 attached base. 



The CalyptrcsidcB are found adhering to stones and shells ; most 

 of them appear never to quit the spot on which they first settle, as 

 the margins of their shells become adapted to the irregularities of the 

 surface beneath. The form and colour of the shell both depend some- 

 what upon the situation in which it grows : those found on the inside 

 of the mouth of dead shells are generally flat or even concave above, 

 and white ; those attached to the outside of shells are convex, and 

 coloured. The animal is supposed to feed on seaweeds and animal- 

 cules. They sometimes cover and hatch their spawn under the fore- 

 part of the foot. 



Vernacular Names. Bonnet, slipper, and cup-and-saucer limpets. 



KEY TO GENERA. 



a. Shell conical, trochiform ; interior with a spiral diaphragm . . CALYPTE.EA. 



na. Shell oval, limpet-like ; interior with a lamina, covering the 



posterior half of the aperture . . . . . . CKEPIDULA. 



Genus 1. CALYPTR.EA, Lamarck, 1799. 



Calyptrmi, Lam., Prodrome Nouveau Class., 1799, 78 : not Lamarck, 1801. 

 Type: C. cliinensis, L. Inf-undibulunt, Sowerby, 1812. Trochita, Schu- 

 macher, 1817. Galerus (Humphrey), H. and A. Adams, 1854. Lepto- 

 notis, Conrad, 1866 (very young shell). (For full list of synonyms see 

 W. H. Dall, U.S. Geol. Survey, Professional Paper 59" The Miocene 

 of Astoria and Coos Bay, Oregon," 1909, 81.) 



Animal having a short head, the muzzle bilobed ; tentacles rather 

 short, cylindrical, with the eyes on tubercles at their exterior base ; 

 foot short, rounded, obtuse behind, angular in front. 



Shell conical, trochiform, with a lateral spiral apex ; aperture 

 basal, circular, entire. ; interior furnished with a spiral basal plate, 

 the coluniellar margin of which is twisted, forming a false umbilicus, 

 free margin convex. 



The Recent species are tropical and subtropical in their distribution. 



Fossil. The genus first appears in the Lower Cretaceous. 



Siibgen. 1. CALYPTR^EA, s. str. 

 Trochaiclla, Lesson, 1830. Clypeola, Gray, 1867. 

 Summit central or subcentral. 



KEY TO SPECIES. 

 a. Shell rather small, thin, conoidal, depressed . . . . . . scutum. 



aa. Shell large, thick, solid, conic, elevated .. .. .. ulta. 



