98 PALEONTOLOGY OF NEW YORK. 



short compared with those of atypical ArHYRisand make but a short curve within 

 the primary himelhe. A very peculiar feature of this structure is tlie absence 

 of an upright athyroid stem, tlie bifurcation of the intercalary lamellae taking 

 place at the point of union of the lateral supports of the loop, the whole 

 apparatus having thus, the form of an inclined X, with its upper tips curved 

 outward. The demonstration of this structure justifies the conclusion of Mr. 

 Glass that the species is not an Athyris, but another of such incipient stages 

 of athyroid structure as are represented by Meristina, Whitkieldella, etc., 

 though lacking the upright jugal stem which all those possess. Mr. Glass has 

 proposed to place the species under Davidson's genus Bifida, where it might 

 perhaps rest, were we confident of the accuracy of the determination of the 

 loop in B. lepida as given by Mr. Davidson (see discussion of the genus 

 Bifida), but ivs the shell certainly represents a distinct variation of structure 

 from any heretofore observed, it will be far more satisfactory to recognize this 

 fact by giving the species some distinctive term, as Glassina. 



Subgenus SPIRIGERELLA, Waagen. 1883. 



1862. Athyris, Davidso.v. Quarterly Journal Geol. Soc. London, vol. xviii, \i. 28, pi. i, fig. 8. 



1863. Athyris, De Kosinck. Foss. Paleoz. tie I'lnde., p. 33, pi. ix, fig. 8. 



1867. Athyris, Vbrcherk. Jour. Asiat. Soc. Bengal, vol. xxxvi, pt. ii, p. 210, pi. ii, figs. I, I a. 

 1874. Athyris, Dkrbt. Bull. Coniell University, vol. i. No. 2, p. 7, pi. i, fig. 7. 

 1883. Spirigerella, Waaobn. Palsontologia Indica, p. 450. 



Dr. Waagen has proposed to separate from Athyris a considerable group of 

 species, under the term Spirigerella. Adhering pretty strictly to the broader 

 characters of the type-species, S. Derbyi, Waagen, it would seem that his asso- 

 ciation of species* under this term is to a certain degree heterogeneous ; at all 

 events, the group conforming in exterior characters to Spirigerella Derbyi, has 

 a peculiar expression not shared by such forms as S. grandis, S. media, S. ovoid- 

 alis, and S. fusiformis, Waagen. 



The distinctive features of Spirigerella are as follows; Exteriorly the 

 shells are elongate, but may be transverse; their contour shows a decided tend- 



* Ten in number, from the Carboniferous rocks of tbe Salt-Range. 



