BRACHIOPODA. 
183 
In the Thirteenth Annual Report of the New York State Cabinet of Natural 
History (1860) some specimens of Rhynchonella 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 
Rhynchonella, 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 Rhynchonellcz, 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 Rhynchonella capax of Conrad, the ventricose shells which, in 
the work cited, were referred to R. increbescens. The latter term was introduced in 1847 for shells from 
the Trenton limestone of New York, which never attain the great gibbosity 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. 
