182 _ TRANS. OF THE ACAD. OF SCIENCE. 
posite valve; mesial ridge, corresponding to the dorsal sinus; 
internal sunfice of ventral valve garnished with a prominent 
trifid cardinal process, fortified at its base with three diverg- 
ing ridges, two extend laterally — — to the cardinal 
line and become obsolete on the the third or thesabie 
ridge, extends perpanidipalarts freak the cardinal a to the 
middle of the valve, where it becomes prominent a 5 
on each side of the last, and in the angles between it and tl 
two former. cena a are — oval rugose scars of the a 
muscles; vascular impressions, ches nearer the anterior and 
lateral karla pate by recurved sinuses to the anterior 
part of the mesial ridge; central pi on of the visceral region 
punctate and marked with longitudinal coste; around the 
anterior border i is a zone, ornamented with tubes, those on the 
Gato 40 far as observed, is confined to the 
oe ny a nsasensis ranges down to the base of the 
Car oa ee i Kans ot were found very abundant by 
make ‘the Geological s survey Se Pantin 
: Proovorus (Strophatoviay Noxwoo Di Swoall si : 
fom nor ar a 
