248 



FORMS OF THE SPIRAL 



Anostoma (Fig. 154), Opisthostoma (Fig. 208, p. 309), Strojiho- 

 stonia, and Hy2)selostoma (Fig. 202 A, p. 302). 



Some genera of the Capulidae, in wliicli the shell is of a 

 hroadly conical form or with scarcely any spire, develop an 

 internal plate or process which serves the ])urpose of keeping the 



Fia. l.'J3. — Sili'jiiaria anr/idna Lam., slinw- 

 iiig scalariforiu coil of upper whorls and 

 irregular extension of the lower. 



Fi(!. l.'J4. — Anostoma (jlohulosum Lam., 

 lirazil. (After P. Fischer.) 



animal within the shell, and does the work of a strong attacliment 

 muscli'.. In Mitrularia this process takes the form of a raised 

 horseshoe ; in Crucihulum it is cup-shaped, with the edge free all 

 round ; in (lalcrus, Ergaeu, Crepijmtella, and Trochita we get a 



Fia. L'jS. — Various forms of the internal plate in Capulidae : A, Calyptraea {Mitni- 

 laria) equestris Lam., E. Indies ; B, Orucibuliim scutellatum Gray, Panama ; C, 

 Ergaea plana Ad., and Reeve, Japan ; D, Galerus chinensis L., Britain ; E, Crepi- 

 patella dUatata Lam., Callao ; F, Trochita maculata Quoy, N. Zealand ; G, Crepi- 

 dula fornicata Lam., N. America. 



seri(\s of changes, in which the edge of tiic cup adheres to tlie 

 interior of the sliell, and tlien gradually flattens into a plate. In 

 Crcpidula proper this plate becomes a regular partition, covering 

 a considerate portion of the interior (Fig. 155 CJ). Hipponyx 

 secretes a tliin calcareous plate on the ventral surface of the foot, 



