NATURAL SCIENCES OF PHILADELPHIA. 37 



ing strife, and a few stronger marks of growth may be observed on well p 

 served specimens, the stria, however, excepting near the front and lateral 

 margins, not being readily seen without the aid of a magnifier. 



Length, about 1-45 inches; breadth, 2-20 inches; convexity, about L5I 

 inches ; height of area at the beak. 0-2(J inch. 



We have had specimens of this fine Spirifer under consideration for a long 

 time, and after numerous careful comparisons, we have been unable to iden- 

 tify it with any of the described species. It seems to be most nearly allied to 

 our common Coal-Measure species S. cameraltis, of Morton, with which it agi 

 in the fasciculated character of its costa?, and in general appearance. It dif- 

 fers, however, in several characters by which it can be readily distinguished 

 on comparison. In the first place, its larger fasciculated costic arc distinctly 

 broader, and rather more depressed on the anterior slope of its valves, and 

 proportionally less numerous. The incurved apex of the beak of its ventral 

 valves is always less abruptly curved, and much more flattened. The most 

 marked character, however, is to be observed in its cardinal area, which lias 

 its margins almost perfectly parallel, instead of being always sloping from th< 

 beak to the lateral extremities. The same characters and its narrow mesial 

 fold and sinus distinguish it from the variety of S. striatus, with somewhat 

 fasciculated costre. It belongs to the subgenus Triffonotreta. 



Locality and position. Keokuk division of the Lower Carboniferous series, 

 at Crawfordsville, Indiana. 



Stricklandinia deformis, M. aud W. 



Shell (internal casts) longitudinally subovate, oblong, or sometimes in 

 young examples nearly or quite as wide as long; valves very nearly equal, 

 and sometimes showing very faint traces of an obscure mesial prominence on 

 the dorsal valve, and of a corresponding depression near the front of the ven- 

 tral valve ; hinge line straight, and less than the breadth of the valves ; sur- 

 face apparently smooth, or only with concentric lines on the young shell, 

 while casts of the adult show so'rne traces of a few obscure, irregular, radiat- 

 ing ridges. Beaks, area and finer surface markings unknown. 



Length of a young internal cast, 1 inch ; breadth, 0-97 inch ; convexity, 0-46 

 inch. Length of a large specimen, 193 inches; breadth, 1-58 inches ; con- 

 vexity, 1 inch. 



This shell varied so greatly in form at different stages of its growth that il 

 is very difficult to give a description that will convey a correct idea of it. 

 Young examples from 0'70 to one inch in length approach a broad obovate 

 form, "being truncated on the hinge line, and somewhat narrowly rounded 

 at the middle of the front ; while their posterior lateral margins are more or 

 less straio-htened and inflected, as we often seen in Rensselaeria. After attain- 

 ing this size and form, the shell, judging from some four adult examples we 

 have seen, seems to have suddenly commenced a more vigorous growth, 

 mainly forward and antero-laterally, so as to attain a much larger size, leav- 

 ing the valves of the young shell, as it were, opened and spread upon the 

 beaks, thus completely destroying the symmetry of the entire shell. At this 

 stao-e of o-rowth the shell has a curious constricted appearance at the con- 

 nection of the young and adult shell ; while the whole breadth posteriorly 

 is onlv that of the young shell, and the widest part is then some distance in 

 advance of this, and the posterior margins are strongly flattened by their 

 sudden inflection towards each other there. 



The casts show that the chamber in the beak of the ventral valve is of 

 moderate size, and supported upon a rather short mesial septum 1 he socket 

 processes are seen, by their impressions in the cast, to be small, not united, 

 and scarcely assuming the character of plates; while the crural pro, ex- 

 tended from their inner lower sides forward nearly parallel so as t< o - 

 slender, deep perforations in the cast. The surface of the young shell appeara 



1870.J 



