BRACmOPODA. 183 



In the Thirteenth Annual Report of the New York State Cabinet of Natural 

 History (1860) some specimens of Rhynchmella increbescens* Hall {==R. capax, 

 Conrad), from the Hudson River group of Iron Ridge, Wisconsin, which pre- 

 served the details of internal structure most admirably, were described and 

 illustrated. 



The essential part of this description (p. 67) was as follows : 

 " This species, like some others of the genus, becomes extremely gibbous or 

 ventricose with age, and the apex of the ventral valve is closely incurved over 

 the beak of the opposite valve. Nor is this all, for the beak is perforate, and 

 in many specimens we are able to discover a distinct foramen in the substance 

 of the shell ; indeed, sometimes this foramen is above or exterior to the apex 

 of the beak, but it is rarely possible to distinguish the continuity of the sub- 

 stance of the shell between this foramen and the beak of the opposite valve. 

 Externally, therefore, this feature might not be considered incompatible with 

 Rhtnchonella, where the base of the foramen is often formed by the beak of 

 the dorsal valve ; and it might be supposed that as the shell increased and the 

 incurvation became too great to permit the protrusion of the pedicle at the 

 ordinary foramen, the notch in the beak might be deepened until it would reach 

 beyond the apex. Sometimes, however, this foramen is seen to be surrounded 

 by the substance of the shell ; thus becoming a simple perforation, without the 

 appearance of deltidial plates. 



" The real condition and relations of this foramen I have recently been able 

 to determine satisfactorily, from an examination of some separated valves and 

 imperfect specimens collected by Mr. Woolson, of Iron Ridge, Wisconsin, from 

 the green shales beneath the iron ore. The interior of the dorsal valve has 

 the usual aspect of this valve of other Rhynchmella, except that in the center 

 of the apophysary process, at the base of the crura, there is a narrow central 

 process which is more distinct than usual. In the ventral valve there are two 

 strong teeth which fit into deep sockets in the opposite valve and above these, 

 the triangular space is partially or entirely occupied by a concave solid area ; beneath 

 which, extending from the interior of the shell, there is a distinct foramen 



* It seems necessary to consider as the Bky^ichonella capax of Conrad, the ventncose shells which, in 

 the woi-k cited, were referred to R. increbescens. The latter term was introduced in 1847 for shells fiom 

 the Trenton limestone of New Yorli, which never attain the great giljljosity common in R. capax, but are 

 not unlike the immature individuals of that species. It seems therefore R. increbescens has no higher value 

 than a designation for an earlier and somewhat modified type of R. capax. 



