448 



MOLLUSCA. 



The only other genus of the Spiriferidce which needs 

 mention here is Atrypa, which may be regarded as in 

 many respects intermediate between the present family and 

 the RJiyncJwnellidce. Though named in accordance with the 

 belief that the beak of the ventral valve was imperforate, a 

 small foramen is really present in this genus (fig. 292), 



Fig. 292. Atrypa reticularis. Upper Silurian and Devonian of Europe 

 and America. (After Billings.) 



sometimes concealed, and sometimes bounded in front by a 

 small deltidium. The spiral brachial processes are large 

 and conical, and are directed with their apices turned into 

 the hollow of the capacious and ventricose dorsal valve. 

 The genus ranges from the Silurian to the Carboniferous, and 

 its type is the cosmopolitan and familiar Atrypa reticularis 

 (fig. 292) of the Upper Silurian and Devonian. 



FAM. IV. KONINCKINID^:. Animal 

 unknown. Shell free ; valves unar- 

 ticulated (?). Oral arms supported by 

 two lamellae spirally coiled (fig. 293). 

 The only genus of this family is 

 Koninckina, represented by the single 

 species K. Leonhardi of the Trias of 

 St Cassian. The shell resembles Pro- 

 ducta in being eared, and the dorsal 

 valve is concave, and follows the 

 curve of the ventral valve. It differs 

 from Producta in having the arms supported upon spiral 

 processes. 



FAM. V. EHYNCHONELLID^E. Animal free, or attached by 

 a muscular peduncle issuing from an aperture situated under 

 the extremity of the beak of the ventral valve. Arms spi- 

 rally rolled, flexible, and supported only at their origin by a 



Fig. 293. Koninckina Leon- 

 hardi, showing the spiral sup- 

 ports for the arms. Trias. 



