502 PALEONTOLOGY OF ILLINOIS. 



BRACHIOPODA. 



Genus STBICKLAKDINIA, Billings. 



Stricklandinia deformis, M. and W. 



PI. 24, Fig. 5 a, b. 

 Stricklandinia- deformis, Meek and Worthen, 1870. Proceed. Philad. Acad. Nat. Sci., p. 37. 



Shell (internal cast) 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 ventral valve ; hinge line straight, and less than the 

 breadth of the valves: surface apparently smooth or only with concen- 

 tric lines on the young shell, while casts of the adult show some traces 

 of a few obscure irregular radiating ridges. Beaks, area and finer sur- 

 face markings unknown. 



Length of a young internal cast 1 inch, breadth .97 inch, convexity .46 

 inch. Length of a larger specimen 1.93 inch, breadth 1.58 inch, con- 

 vexity 1 inch. 



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

 that it is very diffcult to give a description that will convey a correct 

 idea of it. Young examples from .70 to 1 inch in length approach a 

 broad ovate form, being truncated on the hinge line, and somewhat 

 narrowly rounded at the middle of the front ; while their posterior late- 

 ral margins are more or less straightened and inflected as we often see 

 in Rensselaeria. After attaining this size and form, the shell, judging 

 from some adult examples we have seen, seems to have suddenly com- 

 menced a more vigorous growth, mainly forward and antero laterally, 

 so as to attain a much larger size, leaviug the valves of the young shell 

 as it were, open and spread upon the beaks, thus completely destroying 

 the symmetry of the entire shell. At this stage of growth the shell has 

 a curious constricted appearance at the connection of the young and 

 adult shell ; while the whole breadth posteriorly is only that of the 

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

 this, v 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 on a rather short mesial septum. The 



v 



