PEOCEEDINGS OF UNITi:D STATES NATIONAL MUSEUM. 47 



Fig. 1, on Plate , represents one of the examples referred to, tlie 



principal portion of the figure showing a natural cast of the dorsal valve, 

 with the umbonal portion of the ventral valve. In this figure the full 

 length of the shell from back to front is not shown, but it is represented 

 in the accompanying diagram, Fig. 2. 



WASHiNGrTON, D. C, December 3, 1879. 



note: on acrothejlc:. 

 By C. A. IVHITE. 



Among the fossils collected from Primordial strata at Antelope Sprang, 

 Southern Utah, by Mr. G. K. Gilbert and Mr. E. E. Howell, who were 

 then connected with the explorations and surveys west of the 100th 

 meridian, were a number of examples of a discinoid brachiopod. This 

 form I described and figuea* under the name of Acrotretnf suhsidua, 

 referring it to that genus provisionally. None of the examples were in 

 a condition to show all the generic characters clearly, but certain fea- 

 tures in these shells indicated their possession of important differences 

 from any genus then established and led me to suggest that they prob- 

 ably represented a new generic type. In the same year, 187G, Prof. G. 

 Linnarsson, of Stockholm, Sweden, i^ublishedt a new generic form from 

 the Primordial rocks of Sweden, under the name of AcrotlieJe^ which 

 Ijlainly includes Acrotreta f subsidiia White. Professor Linnarsson des 

 cribed two Swedish si)ecics under this generic name {A. coriacea and A. 

 granulata), and in 1879 he published a third species under the name of 

 A. mtermedia^X but A. sulmdua is at present the only known Ameiican 

 species. It is not unlikely, however, that some of the American species 

 heretofore referred to Discina will be found to belong to Acrothele. 



Washington, D. C, February 1, 1880. 



DESCRIPTION OF A NEW CRETACEOUS PINNA FROM NEW 



MEXICO. 



By C. A. WHITE. 



Pinna stevensoni. 



Shell large, elongate-triangular in marginal outline; valves moder- 

 ately convex; the convexity being slight and nearly uniform poste- 

 riorly, but much greater toward the front, where it amounts to an obtuse 

 median angularity upon each valve, and wheie a transverse section of 

 the shell has an approximately regular rhombic outline; upper border 



* Expl. and Sur. West of the lOOMi Merid., Vol. IV, p. 34, pi. I, fig. 3, a, b, c, aud d. 



t BihaDg till k. Svenska Vet. Akad Handlingar, Baud 3, No. 12, p. )iO, pi. IV, figs. 

 44-52. 



tSveriges Geologiska Undersokuiug; Ser. C. Afhaud. och Upps. No. 35, p. 25, pi. 

 iii, figs. 40-44. 



