228 MonograpTi of the LameUihrancliiafa. 



left valve, with sometimes a slight prominence or riidimeutary cardinal 

 tooth just in advance of this pit; while of posterior lateral teeth there 

 is in the right valve one long tooth ranging parallel to, the cardinal 

 margin, with a parallel furrow above and below it, for the reception 

 of two long posterior laterals in the left valve, the lower one of which 

 is more prominent, and the upper merely linear or rudimentary. The 

 furrow between these two posterior lateral Jeetli of the left valve is 

 well defined, and receives the corresponding tooth of the other valve. 

 Below the lower of these furrows, on the posterior side of the right 

 valve, there is a very slight marginal ridge, that may sometimes 

 assume the character of a second posterior lateral, but it is most promi- 

 nent anteriorly, where it connects \vith the cardinal tooth», of which 

 it seems rather to be an oblique posterior prolongation than a distinct 

 tooth. On the anterior side, there is one shorter anterior lateral tooth 

 in the right valve, also ranging parallel to the hinge margin, and above 

 and below this a little furrow for the reception of two small anterior 

 laterals in the left valve, which receive between them that of the right 



valve. 



The pallial line is certainly simple, and the muscular impressions 

 Aveli defined, the posterior one being larger than the other, and pro- 

 vided with a small accessory scar above, just under the posterior ends 

 of the posterior lateral teeth. The ligament or cartilage was probably 

 small and internal, as there are no traces of an external ligament to be 

 seen, the valves fitting close all along the hinge margin. No lunule 

 or escutcheon is to be seen in any of the specimens. 



Found about 300 feet below the Upper Silurian rocks, at Versailles, 

 Indiana. 



Genus TelUnomya — (Hall, 1847). 



[From Tellini and Mya, from the form of the shell.] 



Shell equivalve, equilateral or subequilateral, closed, smooth, or 

 marked by lines of growth ; ligament external; hinge line curved, 

 sometimes subangular, with a continuous series of small curved trans- 

 verse teeth, which diminish from the extremities to the beak, beneath 

 Avhich they are much smaller ; muscular impressions double, two ante- 

 rior and two posterior, one large and strongly impressed, the other 

 smaller, lying above and between the larger one and the hinge line ; 

 pallial impression simple. 



In the larger species known, the hinge line is only slightly arcuate ; 

 while among the other species we find many variations in the curva- 

 ture, and it sometimes becomes distinctly angular, as in T. cuneata. 



