DESCRIPTIONS OF SPECIES. 397 



more common Sjj. hentuckyensis. The shells which Derby," in 1874, and Walcott,* 

 in 188i, in the one case from Brazil and in the other from Nevada, identified as 8p. 

 spinosa, and also that from New Mexico which White " published in 1875 under the 

 name of 82). octoplicata, undoubtedly belong here. As the 3'ear previous, in a 

 preliminary report upon the collections of the One Hundredth Meridian Survey, 

 White had distinguished this form from Sp. spinosa by the varietal name cam- 

 pestris, it has been retained here, but in a specific sense. 



The material studied by me consists of fossils from Colorado, New Mexico, 

 Nevada, and Texas, and includes the types of Meek, of White, and of Wal- 

 cott. The species may be briefly described as follows: The shell is rather large, 

 transverse, the hinge line being usually as broad or a little broader than the 

 width of the shell below. Dorsal valve moderately convex, ventral valve rather 

 elevated with a high area, which is more or less strongly incurved. Fold and sinus 

 simple; on either side are four or five lateral plications. The latter are thin, high, 

 and subangular, and so are the reverse plications and also the fold and sinus, which 

 are only distinguished by being somewhat more elevated than the others. The 

 surface is essentiallj' smooth. Several concentric growth lines, more or less elevated 

 and lamellose, are fi'equently present, but they are sometimes practically absent, and 

 never in frequency and regularity produce an effect similar to the lamellose orna- 

 mentation of shells of the type of Spiriferina Tcentuckyensis and its allies. These 

 markings are usually inconspicuous, and the most striking character of the surface 

 consists in its being covered by numerous rather coarse and sparse hollow spines, 

 which, either by nature or by accident, are seen to be open at the outer end. The 

 spines are more thicklj^ distributed in some individuals than in others, but the range 

 of variation is not excessive. In some, though not in all, a number of spines in the 

 ventral sinus are serially arranged and more or less connected by a delicate ridge. 

 Nothing to correspond with this has been noticed on the fold. The surface under 

 different conditions of preservation presents appearances so unlike that I was nearly 

 misled into subdividing the species into at least two groups variefally distinct. The 

 outer shell la^^er, which is retained onl)' on well-preserved specimens, seems to be 

 itself impunctate, and often completely masks the punctate structure of the shell 

 below. 'It is nearly smooth, except for the tubular excrescences above referred to, 

 being marked b}' delicate, almost invisibly fine growth lines. Under slightly 

 different conditions of preservation the appearance of the surface is very much 

 changed, and the shell appears to be covered by innumerable closely set minute 

 spinules, which are both much smaller, more numerous, and more thickl}^ arranged 

 than the large ones on the preceding. This appearance seems to be due to the 

 removal of the delicate superficial layer and with it the larger spines. The spinules 



a Cornell "Univ., Bull., vol. 1, No. 2, 1874, p. 23, pi. 6, flgs. 8, 13, 14. 



6 U. S. Oeol. Surv., Men., vol. 8, 1884, p. 218, pi. 18, flg. 13. 



c U. S. Geog. Geol. Surv. W. 100th Mer., Kept., vol. 4, 1877, p. 139, pi. 10, flgs. 8a-8o. 



