■i;H) CARBONIFEROUS FORMATIONS AND FAUNAS OK COLORADO. 



of Spirifer sj). h, structures wliich do not occur in Sp. crlspus, Sp. vanuxeml, mid 

 their ;illi(\s. 



On the whuk'. it seeuis more j)rol):ible tiiut this form is a true Spir/fi'i; a survivor, 

 possibly, of the earlier tj'pe abundant in Silurian and early Devonian time, one 

 which departs so far from its nearest allies, the unicispinei, that it can hardly with 

 propriety be referred to the same subordinate group. Indeed, if the appearances 

 described are real characters of the shell, and of this 1 have little doubt, it can only 

 be regarded as an aberrant member of any of the groups recognized by Hall and 

 Clarke, and should other species possessing similar charactei's be brought to light, 1 

 believe they would better be recognized as an independent section. The salient 

 characters of this form which would probably applv in lai-ge measure to the whole 

 subsection are its small size, primitive shape (like that of Deltliyris)^ short hinge 

 line, spinose surface (the spines not being mounted upon the edges of concentric 

 lamella?, which are in fact practically absent)," the absence of a septum in the ventral 

 valve, and the presence of dental lamellse in both valves. 



The stratigraphic significance of this species depends chiefiy upon which spiri- 

 feroid group it is conceived to be closest allied to. In my own view its affinities 

 with any of the known groups of American spirifers is so remote that its bearing in 

 that relation can not yet be estimated. In this connection attention may be called to 

 Sp. agelakm Meek, which may possiblj^ be based upon small or immature shells of this 

 species. The similaritj' is not so great as to be impressive, but our lack of knowledge 

 regarding the minutiae of Meek's species does not permit a decision in the negative. 

 The most closely allied species which I have been able to find, however, is a little shell 

 from the Louisiana limestone of Missouri, described hy Rowley under the name Spirifer 

 01- Spiriferina aciculiferafi This species also is a spine-bearer, but as its internal 

 structures are not known no comparison with the Colorado form can be made in this 

 direction. It is improbable that Rowley's species is a true Spvriferina. Rowlej^ 

 has recently described another little shell which is externallj^ similar to the form 

 from the Leadville limestone. I refer to Sp> ir if er schitcher^ti" "which y^^s found in 

 the Lower Burlington limestone at Louisiana, Mo. Though a somewhat smaller 

 form, the essential superficial resemblance is markedj but it is uncertain whether the 

 internal characters would show an equal agreement. 



In configuration this species simulates the form referred to Spiriferina solid- 

 irostris, though it differs from the lattei' in everj^ essential particular. The two 

 forms can usually be discriminated even superficially, however, as Spirifer sp. 5 has 

 rounded cardinal angles and a more distinct median plication on the fold and sinus, 



aThe surface ornamentation evidently varies somewhat in different individuals in regard to the shape of the spines, 

 their abundance, and arrangement, but all specimens agree in showing the essential absence of lamellose striae as a 

 normal system of surface ornamentation and the abundance of minute, simple, hollow spines. 



;> Am. Geologist, vol. 12, 1893, p. 307, pi. 14, figs. 13, 14. 



cAm. Geologist, vol. 25, 1900, p. 261, pi. 5, figs. 15, 16, 17, 59. 



