10 



Indiana University Studies 



sinuate beneath the beak and nearly straight below until the vicinity of the 

 venter is reached, when it joins the curve of the base. The surface is orna- 

 mented with fine concentric laminae with an occasional coarser one. The 

 beak shows strong lines of growth. 



The following measurements are of an immature specimen in which the 

 fullness of the peculiarities of the shell are not well brought out. Larger 

 specimens have these features much more accentuated. However, since it 

 is the only specimen at hand that is nearly perfect, it is used. Length of 

 hinge, tip of beak gone, 58 mm.; total length about 63 mm.; height of shell 

 65 mm.; greatest length of shell below the hinge 31 mm.; width of hinge 

 plate on larger specimen 6.5 mm. 



Fort Riley limestone; Blue Springs, Nebraska. It also occurs as low as 

 the Eskridge shales, at Grand Summit, Kansas. 



This species is closely related to M. aviculoidea Meek, but our shells 

 appear to have been flatter while the lines of growth show a distinct sinuosity 

 on the posterior side in specimens smaller than the type of Meek's species. 

 Moreover, specimens from Texas seem to show that the species are clearly 

 distinct. The shells are far from rare in a bluish clayey limestone at the 

 quarries at Blue Springs, but complete specimens were very difficult to secure 

 at the time of my visit there. Indeed I do not remember of having seen a 

 large perfect cast. One peculiar thing about it is that the larger part of the 

 shell is frequently shown in these specimens, but some part is usually missing. 

 There is no likelihood of confusing this species with any other shell. 



Pleurophorus beckwithi n.sp. 



Shell small, elongate, slightly higher posteriorly than in front. The beak 

 is somewhat removed from the anterior end on account of a distinct forward 

 prolongation of the shell in the region of the anterior adductors. The hinge 

 is gently arcuate and the posterior end is not truncated, but rounds with 

 very narrow curve into the ventral margin, which is straighter than the dorsal 

 border. The anterior end is very sharply rounded below and slopes obliquely 

 backward and upward to the beak in the upper half of the shell. The umbonal 

 ridge is not well developed and the depression obliquely below the beak is- 

 wanting. The posterior lateral tooth is well developed, and one long tooth 

 projects forward just below the beak, while there is a socket just as large 

 above it. The adductor scar is small but prominent, and is separated from 

 the rest of the shell by a short, broad ridge. No pedal scar is visible in the 

 cast. Surface ornamentation is unknown. Height of the cast at the beak 

 4.5 mm.; length 11.5 mm.; beak 1.5 mm. from anterior end. 



Double Mountain Beds(?) Permian; "Buckle L" Ranch, at the top of the 

 breaks about a mile east of the west fence, and two and a half miles south 

 of the north fence. Calcareous sandstone bed. Cottle county, Texas. 

 Collected by H. T. Beckwith. 



Deltopecten ballingerana n.sp. 



The shell is large, nearly as high as long, rather convex, slightly oblique, 

 with the hinge nearly as long as the shell. The ears of the left valve are 

 large, the anterior one being separated from the shell by a rounded, rather 

 indefinite sulcus, with considerable marginal constriction below it. The 

 posterior ear is apparently somewhat longer than the anterior one, and 



