Maryland Geological Survey 403 



Spirifer vanuxemi Hall 

 Plate LXVIII, Figs. 32, 33 

 Spirifer vanuxemi Hall, 1859, Nat. Hist. N. Y. Pal., vol. iii, p. 198, pi. viii, figs. 

 17-23, 1861. 



Description. — " Shell rhomboidal, moderately gibbous : extremities 

 rounded. Ventral valve the less convex, having the beak elevated and in- 

 curved. Area small. Surface marked by broad rounded or somewhat 

 flattened and sometimes undefined plications, of which there are from two 

 to four on each side of the mesial fold and sinus ; concentrically marked by 

 fine closely arranged undulating stria) and stronger imbricating lines of 

 growth, which are again crossed by still finer radiating striae ; the latter 

 visible only under a magnifier." Hall, 1859. 



The individuals referred to this species in Maryland differ somewhat 

 from the typical >S'. vanuxemi of the ]\Ianlius of iSTew York in their ex- 

 pression, although the differences hardly justify a distinct varietal name. 

 They appear to be confined to the Chonetes jerseyensis zone. 



Occurrence. — Helderbebg Formation, Keyser Member. Devil's 

 Backbone beneath the Gypidula zone, Cash Valley, IJ miles northeast of 

 Flintstone, Eoundtop. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



[Maynard.] 



Spirifer vanuxemi var. prognosticus n. var. 

 Plate LXVIII, Figs. 34, 35 : Plate LXIX, Figs. 1-3 

 Description. — The variety prognosticus differs from ^b". vanuxemi in that 

 matured examples have from five to six plications (young ones have from 

 three to four) on each side of the dorsal fold, while in Maryland examples 

 the latter has from three to four. Otherwise, the general expression is the 

 same in both. This variety is a continuation of the Manlius 8. vanuxemi 

 and is prophetic of S. cijclopierus which it resembles in its general ex- 

 pression. The latter form, however, is always larger and may attain a 

 size more than twice that of the ^axieiy prognosticus, yet it has but eight 

 plications on each side of the dorsal fold. In mature forms of S. 

 cyclopterus the plications vary between six and eiglit, and the cardinal 



