462 Troxell — Unios in the Trias sic af Massachusetts. 



characters would be less marked if the shell could be viewed 

 from the outside. The largest specimen, a cast of the inside 

 of the left valve, has an internal length of 47 ram , is 22 mm high, 

 with a body cavity, including both valves, 10 mm wide. The 

 muscle scars and large hinge teeth, so far as they can be 

 determined, are shown in the illustration, figure 2a. 



A second specimen of U. emersoni, shown in figure 3, is an 

 interior cast of the valves, connected and considerably opened. 

 The section of this specimen (fig. 2c) is taken through the 

 umbones. 



In none of the specimens on the slab is there a trace of the 

 original shell ; the fossils are merely the molds of the body 

 cavity. 



The new species is named after Professor B. K. Emerson, 

 who has spent so many active years in deciphering the difficult 

 geology of western Massachusetts. 



The presence of this second species of Unio was first noted 

 by Professor Charles Schu chert, while Professor R. S. Lull in 

 his memoir on the Connecticut valley* first designated the 

 specimen as U. emersoni. As this is a nomen nudum, the 

 writer was asked to describe the species, and he takes this 

 opportunity to thank the gentlemen mentioned for this privi- 

 lege. 



*Bull. 24, Conn. Geol. Nat. Hist. Surv. (in press). 



