30 MEMOIRS OF THE STATE MUSEUM 



Streptis WALDRONENSis, Miller and Dyer, 1878 



Plate III, Figs. 9, 10 



Spiriftraf ■waldronensis. Miller and Dyer. Contributions to Palaeontology, Jour. Cinti. Soc. Nat. 



Hist.. April. 1878. 

 TrifiUsia puliilus. Hall. Trans. Alb. Inst., vol. x, Abstract, p. 16. 1879. 

 , Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 298, pi. 27, figs. 19-22. 1882. 



This species is among the rarest of the Waldron brachiopoda 

 and it is impossible to present a series representing the variety and progress 

 of development, as in some of the more common forms. There were but 

 two specimens, both adults, discovered in the State Collection at the time 

 of the publication of the " Descriptions of New Species of Fossils from 

 the Niagara Formation at Waldron, Indiana."* Fortunately, we have 

 more recently detected a young individual of about one-fourth the normal 

 adult size, which offers some interesting details in its form and characters. 



The asymmetry of the shell is manifest even at this early stage of 

 growth (although the median fold is not developed), and is evinced by the 

 position of the beak of the ventral valve, and by the contour of the margins. 

 It is probable that in a still earlier phase of growth, the two valves are 

 symmetrical, or nearly so. 



In the young individual under consideration (plate 3, figs. 9, 9^7, 9/;), 

 the outline is nearly circular. The beak of the ventral valve is very much 

 elevated, projects beyond the cardinal line and is directed toward the 

 left side of the shell. The apex is truncated, and the opening is confluent 

 with the area below. ^ 



The cardinal area is high, forming a large triangular fissure which 

 is apparently not closed by deltidial plates. The beak of the dorsal valve 

 is depressed, and limited by a slight furrow on each side. No lines of 

 growth are visible, but the surface is somewhat granulose, as in many small 

 shells of other species. 



♦James Hall. Read before the Albany Institute, March 18, 1879. 



