"JM!S CAKHONIKKKonS FORMATIONS AND KAUNAS OK COLORADO. 



Ill iicitlici- \;ilv(> is II septum dcNi'lopcd, and llic (lor.siil as well as the ventral 

 shell is runiished with diMital plates. In most \'enlrals, though the dental ])lates are 

 moderately strony. there is no trace. e\'en. of a septum. In others, a shallow groove, 

 ■\vhieh eaii sometin.es he made out, ])roves that tliis structure was ,sometime.<5 present, 

 although insig'niticant. Several s])ecimens agree in siiowing that the dorsal \alve 

 jDossessed dental plates develop(Hl to almost as great a degree as in the \cntral one. 

 No apical callcsity can be seen. 



The surface is practicalh' free from radiating or concentric stri;\?. Sometimes 

 ■\arices of growth occur, and often a marginal band of varj'ing width is marked by 

 concentric lamellosities, but most of the surface is essentially smooth in this regard. 

 It is, however, shown to be finely pustulose or spinose. This is cleai'ly seen in casts 

 of the exterior. In one specimen the holes which the si^ines have left in the matrix 

 are closed by tiny plugs of rock, the shelly matter being represented by rings of 

 Avhite about them. This would seem to indicate that the spine was hollow. Another 

 example, equally favorable, shows only rows of perforations. Several other speci- 

 mens, while disclosing the spinose character of the surface in an unmistakable man- 

 ner, do not give clear evidence as to whether the spines were solid or hollow, but the 

 opinion resulting from a careful study of all the material is that they were hollow. In 

 the specimen iirst mentioned thej'^ are arranged in alternating concentric rows, the 

 lateral distance between any two adjacent elements in the same row being distinctly 

 less than the diagonal distance between those in adjacent rows. Along the anterior 

 margin, where overlapping lamellse occur, the}' are more crowded and irregular. In 

 other shells they are sometimes closelj' arranged and irregular, but usually a c^uin- 

 cunx assemblage can be made out. The shape of the spines is oval or elliptical for 

 the most part, with often a linear projection at one end or the other, and in less dis- 

 tinct preservation the surface of the cast looks to be traversed by very fine inter- 

 rupted striEe. 



The afiinities of this shell are puzzling. The absence of a septum and the pres- 

 ence of well-developed dental lamellte in the dorsal valve would seem to forbid its 

 being referred to Spiriferina in spite of the superficial resemblance to members of 

 that genus. If admitted into the Spiriferina group, however, it would, by reason 

 of its surface, be more closely allied to 82)- s2)inosa than to the hentuchyensis section, 

 but as to its specific distinctness from Sj). spinosa itself there can be no question. 

 The spines are finer and more numerous, and the fold and sinus show a median 

 groove and ridge, not to mention differences in shape and others of a like nature. 

 But besides these superficial differences its structural ones, already pointed out, are 

 of a sufficiently fundamental character to bar it from the genus Spiriferina altogether. 

 It seems, therefore, that its place should be sought among the true spirifers. It does 

 not, however, agree satisfactorily with any of the six divisions of Spirifer recog- 



