DESCRIPTIONS OF UPPER LIAS FOSSILS. 419 



It is represented by three specimens. The central, or what I call the 

 branchial, region in this shell is alone furnished with plications, leaving 

 the pedal and anterior and the siphonal and anal regions or wings smooth. 

 The normal number of plications is nine, specimens as a rule varying 

 but little more or less on either side of this. The species described by 

 Gabb* as Pholadomya nevadana from the neighborhood of Walkers lake, 

 Nevada, is apparently identical with this, having the same number of 

 central plications. The figure is slightly misleading, judging from the 

 descriptions. The type has not been found in any of the collections ex- 

 amined by me. 



Pholadomya multilineata. 



Pholadomya miUtilineata, Gabb. Am. .Jour. Conch., vol. v., p. 10, pi. 5, fig. 6. 



Loc, Beaver creek. 



This species is not closely allied to P. nevadana in general outline, 

 the anterior region of the body being shorter and the umbones situated 

 nearer the anterior ends of the valves. The posterior parts are usually 

 more elongated and broader in their ventro-dorsal diameters. The num- 

 ber and size of the plications diff'er very much from those of Nevadana. 

 They are finer, closer set and more numerous, covering all of the central 

 regions of the valves, leaving only the anal or wing regions and a small 

 part of the siphonal regions smooth, and in the anterior parts of the 

 valves the"oral region alone is smooth. 



Gabb described this species from volcano near Walkers lake, Nevada, 

 and the original has been found in the Whitney collection. Museum of 

 Comparative Zoology. 



Pleuroinya concentrica, n. s. 

 Loc, Beaver creek (?). 



A well preserved specimen occurs of this genus with plainly accented 

 concentric ridges evenly distributed over the entire surface of the valves. 

 The umbones are situated anteriorly low and the umbonal ridges are 

 very gibbous. The jDOsterior or anal hinge line is extended and almost 

 straight. The anterior parts are very short but rounded, and the mar- 

 gins along the pedal and branchial regions are prominently and evenly 

 curved outward without any sinus. This shell may be equivalent to 

 part of Myacites subcompressuSj Meek, but the anterior outline seems to 

 be quite distinct. 



* Am. Jour. Conch., vol. v, p. 10, pi. 5, fig. 7. 

 LIX— Bull. Geol. Soc Am., Vol. 5, 1893. 



