21G 



Some Develoi'mental Stages of Oktiiuthetes Minutus X, Sp. 



By Edgar R. Cumings. 



The specimens discussed in lliis pnper are from the abandoned quarry 

 known as the Cleveland Stone Company's quari-y, located one mile north 

 of Harrodsburg', Monroe County, Indiana. This quarry is in the so-called 

 Bedford limestone, and the specimens come from the top of the quarry— 

 and also from near the summit of the formation. They are, so far as I 

 can ascertain without having seen the original specimens of Hall,* specifi- 

 cally the same as Spergeu hill forms referred by the latter gentleman to 

 the Orthis (Terebratulites) umbraculum of Schlotheim.f 



Description of the shell: 



Shell semiovate to subquadrate in old individuals; hinge line usually 

 less than the greatest width of the shell, especially in young individuals; 

 cardinal extremities forming an obtuse, or sometimes a right angle with 

 the lateral margins. Surface finely plicated; plications increasing toward 

 the margin by interstitial addition. Crests of the plications crenulated by 

 equally spaced fine concentric lines. 



^'entral valve concave with a pronounced tendency to irregular growth 

 about the beak. In mature individuals the beak becomes strongly retrorse 

 and is greatly elevated, equaling in height one-half the length of the shell. 

 Area well defined, Hat. shoM'ing in well preserved specimens a low ridge 

 on each side of the prominent deUidium and parallel with its margins. 

 Tl:e younger specimens seem to show a perforation at the apex of the 

 deltidium. 



Dorsal valve regularlj' convex, greatest elevation about one-third of 

 the way from the beak to the front margin, though -there is considerable 

 variation in this respect in shells of different age. Usually some flattening 

 at the cardinal extremities. Area very narrow or usually scarcely at all 

 conspicuous. 



Interior of the ventral valve showing rathei' prominent teeth, which 

 diverge widely. Cardinal process in the dorsal valve elevated, projecting 



"Acting under the impression that some of the original specimens of Hall were in the 

 Albany Museum, the writer sent a number of specimens of the form under cons'deration to 

 Dr. John M. Clarke to compare with Hall's specimens. AVhile owing to the fact that Hall's 

 specimens are not at Albany, Dr. Clarke could not make the comparison, nevertheless he 

 gives it as his opinion that the two are prohahly identical. 



tPetrefk. I, 256; Schnurr, Brachiop. der Eifel 216; Bronn Lethaea Geog. I, 361. See 

 Hall, Trans. Alb. Inst. 4, p. 12. 



