21 



Genus 4. CRUCIBULUM, Schumacher. 



Animal ; similar to that of Calyptrsea, but with the foot larger 



and rounded. 

 Shell ; ovate or orbicular, sometimes depressed, sometimes conoid, 



radiately ribbed or ridge-striated, sometimes spined, with the 



top mostly near the centre ; internal appendage cup-shaped, 



sometimes laterally compressed. 



This genus, founded in 1817 by the eminent astronomer and naturalist 

 Schumacher, is retained for that section of the Lamarckian Calyptraa in 

 which the internal appendage takes the form of a cup ; and it is sometimes 

 free and sometimes laterally compressed and attached. Concomitant with 

 this there is a marked generic difference in the shell compared with the 

 Calyptrcece proper, being of more solid growth, and having no trace of 

 transparent thread-like tissue. It differs, nevertheless, remarkably accord- 

 ing to locality, mode of attachment, and situation of habitat. A few of 

 the species have been described several times over, especially C. spinosum. 

 Sometimes the shell of this species is largely spined, sometimes only fur- 

 nished with fine prickles ; sometimes it is stout and convex, sometimes 

 almost flat, and the colour is equally variable. Without an extended series 

 of individuals from all parts of its geographical range it is impossible to 

 determine the limits of such a species satisfactorily. 



The Crucibula eminently belong to the New World. One or two small 

 species have been collected in the Eastern seas, but all those of mark are 

 from California and the western shores of South and Central America. 



Figure. 



Grucibulum rugosum. PI. 23. Fig. 134. Shell of an unusually deep 

 bonnet-shaped species, showing a large, well-defined, internal cup. 



