WHiTEAVES.] LARAJHE AND CRETACEOrS IXYERTEBRATA. 61 



below. The tyjjc and only sjiecimen known of the Unlo Alhertensis of 

 the "Willow Creek Series," described on page 3, l0(iks very much like 

 an immature shell, and it is not impossible that TJ. consuetm may 

 ultimately prove to be the adult state of that species. There is 

 also a considerable resemblance between the (july perfect specimen 

 known of U. conmetm and the C Cuuesi of Dr. C, A. White, as tigm-ed 

 on plate 27 of his "(Contributions to PaheontoLigy,' (Xos. 2-8) 

 published at Washington in 1880, under the auspices of the U. S. Geo- 

 logical Siuwey. 



SPH.ERini F0R5I0SUM ? Meek and Hayden, Var. 



Plate 9, fig. 3. 



Ci/c?a.? /or»iO.?a, Meek and Hayden. 1856. Proc Ac. Nat. Sc, Phil., vol. Vlll. 



p. 11.5. 

 Cticlas fragilis, Meek and Haj'den. lb. 

 S/jIutriumformonim, Meek and Hayden, 1860. lb., vol. XII. p. 1S5. 



G. M. Dawson, 1875. Eep. Geol. and P^es. 

 Vic. 4'.)th Parallel, p. 119. 

 " •' Meek. lS7iJ. Eep. U. S. Geol. Surv. Terr., vol. IX., p. 526., 



pi. 43, figs. 4, a, b, c. 



Shell small, moderately convex, most prominent above the middle, in 

 the umbonal region, a little longer than high ; anterior side short and 

 narrowly roumted ; posterior side broader and slightly rounded or very 

 faintly subtruncated vertically, or at nearly a right angle to the poste- 

 tior end of the hinge line, at its extremity. Superior border straight 

 and nearly parallel with the ventral margin behind the beaks, — 

 descending abruptly, obliquely and somewhat concavely in front of 

 them ; venti-al margin broadly and regularly rounded ; umbones tumid, 

 beaks obtuse, raised very little above the highest level of the hinge 

 margin and placed slightly in advance of the middle. 



Surface marked with numerous, minute, close-set and regularly dis- 

 posed concentric, raised striae, which can scarcely be seen without the 

 aid of a lens ; also by a few distant lines of growth. Hinge dentition 

 and muscular impressions unknown. 



Length of the most perfect specimens, six millimetres and a half; 

 maximum height of the same, five mm., and a half 



Ed. Mahan's Coulee, G. M. Dawson, 1881 : apparently abundant but 

 very badly preserved. Belly Eiver, eight miles above Coal Banks, T. C. 

 Weston, 1883, a few single valves. 



By an accidental oversight no mention was made of this little 

 SpJmrium in the enumeration of the fossils of the "Western Laramie" 



