580 Contributions to Invertebrate Palaeontology. 



also more abundant, often showing three ranges on parts below 

 bifurcations. On direct comparison of the Newtonville specimens 

 with specimens from Chester, III., these differences, especiall}' those 

 pertaining to the mode of growth, are very marked and characteristic. 

 Formation and Locality. — In the Maxville limestone (Chester), 

 at Newtonville, Ohio. Collected by Prof. E. B. Andrews. 



BRACHIOPODA. 

 Genus STREPTORHYIVCHUS King. 



Streptorliyncliiis crassuin. 



Plate XIII, figs. 11 and 12. 



Hemipronites crassum M. and W. 



Orthis Lasellensis McChesney, New Pal. Foss., 1859, p. 32, pi. i, fig. 6. 



Shell very variable in size and form, but usually more or less plano-convex 

 as seen in profile, somewhat semi-oval in outline, biit usually a little too long 

 from beak to base to be strictly so considered. Ventral valve more or less 

 flattened, a little prominent on the umbo, but usually becoming slightly con- 

 cave toward the front of the shell ; cardinal area of moderate height with a 

 covered deltidium ; beak more or less distorted. Dorsal valve convex, often 

 quite rotund, but usually depressed convex, with a slightly prominent umbo. 

 Surface of the shell marked by radiating strial of considerable strength, which 

 are sometimes sharply elevated and uniform, but on other specimens may be 

 distinctly alternating in strength or arranged in fascicles ; these are crossed 

 by fine concentric strial which give a finely crenulated surface when viewed 

 through a lens. Coarser concentric umiulations of growth also mark the shell 

 at irregular distances. 



The individuals referred to this species are so extremely variable 

 in all their characters that it becomes next to impossible to properly 

 characterize the species by any kind of verbal description. There 

 are, however, two distinct types of shell included among them, 

 which possess characters sufficiently distinct to indicate. One of 

 these is strongly plano-convex in profile, the dorsal valve being 

 very highly convex, with a large and strong beak, incurved; the 

 ventral valve usually being distinctly concave toward the front 

 margin, and the beak usuall}^ more or less distorted and twisted. 

 This form generally attains a considerable size, occurring of a 

 diameter of two and a half or three inches. The other form is 

 much smaller, seldom exceeding one and a iialf inches in its trans- 

 verse diameter; the sliell is less convex, in fact never very highly 

 rounded, the cardinal area much narrower and the beak less liable 



