496 GEOLOGICAL SURVEY OF THE TEEEITORIES. 



to the latter. Internal casts show the muscular and pallial impressions 

 to be well defined, and the latter to be a little straightened, or showing 

 a very faint tendency to form a small sinus under the posterior. 



This is a rather small and an unusually thin shell for the genus Cyrena, 

 being', as already remarked, much more like a Sphcerium in these char- 

 acters. It is quite abundant at the locality, but as it is only found in an 

 indurated clay matrix, good specimens are with difficulty obtained, and 

 from these the thin shell is very liable to break and scale off, leaving 

 only the internal cast remaining. 



Among the specimens collected there are some of a flaore transversely 

 oval form and somewhat larger size than those I have regarded as the 

 types of the species here described. These may belong to a distinct 

 species, but they agree so nearly in all other known characters that 

 I am at present inclined to regard them as merely a variety of the 

 same. 



Locality and 'position. — Carleton's coal-mine, Coalville, Utah. Creta- 

 ceous. 



PHAEELLAf Pealei, Meek. 



Shell elongate-oblong, or subrhombic, the length being about twice 

 and a half the height, rather compressed ; anterior margin slightly 

 sinuous just in advance of the beaks above, and somewhat narrowly 

 rounded below this faint sinuosity; posterior margin truncated, with a 

 convex outline, very obliquely backward and downward, from the 

 posterior extremity of the hinge to the prominent and very narrowly 

 rounded or angular i^osterior basal extremity; hinge-line proper 

 apparently, comparatively short, and not forming any angularity of out- 

 line at its connection with the sloping posterior dorsal margin ; beaks 

 rising a little above the hinge-margin, but rather depressed and placed 

 about one-fifth the entire length of the valves from the anterior margin ; 

 basal margin long, slightly sinuous along most of its length ; posterior 

 dorsal slopes rather prominently rounded from the beaks obliquely to 

 the posterior basal extremity. Surface only showing obscure lines of 

 growth. 



Length, 1.20 inches ; height, 0.48 inch ; convexity, 0.28 inch. 



Knowing nothing of the hinge of this shell, I only refer it provisionally 

 to Pharella. It does not seem to have had the extremities gaping as in 

 that genus; but the specimen has evidently been accidentally com- 

 l)ressed, and this may have given the valves the appearance of being 

 closed. In general appearance it resembles Solen Guerangeri, d'Orbigny, 

 which seems to belong to the genus Fharella. Our shell, however, 

 evidently differs from d'Orbigny's specifically, at least in not having the 

 posterior margins of its valves near so abruptly truncated, but rounding 

 and sloping forward gradually into the dorsal outline above. Possibly 

 I should call it Modiola Pealei. 



Locality and position. — Missouri Eiver, below Gallatin City, Montana. 

 Cretaceous. 



CORBXILA NEMATOPHORA, Meek. 



Shell of about medium size, ovate-subtrigonal, nearly equivalve and 

 moderately convex, with height equaling two-thirds the length ; anterior 

 outline rounded ; base semi-ovate ; posterior extremity somewhat pro- 

 duced and subangular or minutely truncated in outline below; dorsal 

 outline sloping from the beaks, the anterior slope being more abrupt, 



