32 



GASTEROPODA. 



Fam. 18. CALYPTEyEiD^. — Shell limpet - shaped, with a 

 more or less spiral apex ; interior simple, or divided by a 

 shelly process to which the adductor muscles are attached. 

 With the exception of the persistent genus Cajndus, it is 



Fig. 419. — FLssurellidiB, Calyptrwidse, and Patellida. a, Fissurella IciMata— Eocene ; B, 

 Rimula Blainvillei— Eocene ; c, Kmargimda Guerangueri — Cretaceous ; d, Hipponyx cornu- 

 copioi — Eocene ; e, Crepidula costata — Miocene ; r, Mctoptoma imbricata — Carboniferous ; g, 

 Patella costaria — Eocene. 



doubtful if any of the Calyptrwidcc are to be found in the 

 Palaeozoic rocks. They are by no means abundant in the 

 Secondary formations ; and though more plentiful in the 

 Tertiaries, they attain their maximum in existing seas. 



The genus Calyptrma includes the so-called " Cup-and- 

 saucer Limpets," in which the interior has a half-cup-shaped 

 process attached to the apex of the shell, and open in front. 

 With doubtful exceptions, the fossil species of Calyptrma are 

 all of Tertiary age. In the genus Crepidula (fig. 419, e) 

 there is a shelly partition covering the posterior half of the 

 interior of the shell. The fossil species date from the Eocene 

 Tertiary. 



Hiiiponyx (fig. 419, d) comprises thick and obliquely con- 

 ical shells, with a posterior apex, and provided with a shelly 

 basis marked by a distinct horse-shoe-shaped muscular im- 

 pression. The genus ranges from the Cretaceous period to 

 the present day. 



