Bekde.] Carboniferous Invertebrates. 71 



Measurements : Length, 1") mm. ; width, 28 mm. ; convexity, 

 5 mm. 



Range and distribution : Common throughout the Coal Meas- 

 ures ; from Kansas City to Topeka and Manhattan, Grand Sum- 

 mit, etc. 



There are two specimens from Grand Summit, Ivan., which 

 show a remarkable variation from the average specimens of this 

 species. In these the ears are elevated, distinctly and deeply 

 notched, the lateral margins curving inward, then, making an 

 acute angle, are directed outward and backward to the hinge 

 tip. In all other respects, so far as can be determined from the 

 exterior appearance, they are exactly like the above species. 

 Two other specimens from eastern Kansas also show this re- 

 markable characteristic, though in a less pronounced manner. 



This species differs from the preceding in possessing radiat- 

 ing striae on the surface of both valves and a thicker shell ; it 

 is more broad, and the ridges on either side of the mesial sinus 

 are less prominent. 



Chonetes mesolobus. Plate IX, tigs. 3, 3b. 



Cho/if trs mesofobua Norwood and Pratten, Jour. Acad. Nat. Sci. Phil., in, 

 p. 27, pi. ii, f. 7, (1854): White, Wheeler's Geog. Surv. West 100 Mer., 

 iv, p. 123, pi. ix, f. 7, (1875); etc. 



Shell small, broader than long, moderately convex, trans- 

 versely subelliptical or subquadrate in outline ; hinge line a 

 little more than equal to the greatest width of the shell. Mesial 

 -inus extending from near the beak, broadening and deepening 

 to the anterior margin, bifurcating near its origin and enclosing 

 a mesial fold. Anterior margin nearly straight or slightly sinu- 

 ate ; antero-lateral margin sharply rounded, then passing nearly 

 in a slightly convex line directly backwards to the hinge line, 

 making a slight outward turn before joining it. Cardinal area 

 narrow, foramen broad and shallow, nearly rilled by the small, 

 trifid process of the other valve. Surface ornamented with 

 fine radiating stria', rather coarsely and sparsely punctate. 

 Four or five small spines on eather side of the beak point 

 obliquely backward from the hinge line. The markings on the 

 interior of the ventral valve are rather similar to the preceding. 



