42 Annals of the Carnegie Museum. 



height 28 mm.; ratio I : .635. Width of a smaller individual 38 mm.; 

 height 23 mm.; ratio i : .6. 



Valve of pedicle flattened toward the sides, with a moderately deep 

 sinus, which starts from the beak. Sinus flat, and bordered by a single, 

 usually prominent, rounded plication on each side. Four or five 

 distinct, evenly spaced, rounded plications in the sinus, and on a few 

 specimens one or two faint plications on the sides of the valve. 



Brachial valve convex, with a prominent flat-topped fold, which 

 starts from the beak, and is composed of five or six rounded plications. 

 One or two very low plications are visible on the sides of the valve in a 

 few specimens. 



This species diff'ers from Leiorhynchus utahense var. ventricosum, 

 with which it is associated in the field, in its greater width in relation 

 to its height; in the lesser convexity of the valves, and in the possession 

 of a greater number of plications in the fold and sinus. 



One specimen referred to this species was collected by Dr. Raymond 

 in 1905, and eight specimens were collected by the writer in 1912 from 

 the base of the gray limestone, number 4, and the upper limestone in 

 green shale number 5, in the east and west valleys north of Three 

 Forks. In 1913 two well-preserved specimens were obtained from 

 this same horizon near Sappington, and a few were obtained from 

 Logan, and Lombard. The type is in the Museum of Comparative 

 Zoology. 



14. Leiorhynchus mesacostale Hall. 



Leiorhynchus mesacosialis Hall, 1867, Pal. N. Y., Vol. IV, p. 362, PI. 67, figs. 



18-25. 

 Leiorhynchus mesacostale Raymond, Ann. Carnegie Mus., Vol. V, No. 2, 3, 



1909. 



Fossils referred to this species are fairly common in the limestone 

 and green shale of member number 5, at all of the localities. These are 

 all rather small flattened forms, with the plications limited to the fold 

 and sinus. There are usually three plications in the sinus and four 

 in the fold, but the number is rather variable. They are all evenly 

 spaced, and in that respect difi"er from L. mesacostale as figured by 

 Hall. In general appearance they resemble Camarophoria subreni- 

 formis which is described by Tschernyschew from the Ural Mountains, 

 but without material for comparison it is not possible to tell how closely 

 these forms compare. 



