DESCRIPTIONS OF INVERTEBRATE FOSSILS. 51 



lacruni than in the others, the primaries subtended by 

 secondaries for the most part in polyj^onal strings; surface 

 of test closely granulated in the intervals between tubercles 

 on both ambulacral and interambulacral are;e. 



Measurements. — Height of test 11, breadth 25, greatest 

 breadth of periproct 3.5, breadth of peristome (about) 7 or 

 8 mm. 



Occurrence. — The type of this species was obtained from 

 the Choctaw limestone, south of the Denison-Bonham road, 

 near the lime-kiln about a mile east of Denison, Texas. It 

 was associated with Exogyra arietina, Ostrea quadruplicatu, 

 O. siihovafa. Lima ivacoensis, Pholadomya sancti-sabcv, 

 P. ragsdalei, etc. 



The writer takes pleasure in naming this interesting 

 echinoid after his friend and sometime fellow-traveller, Prof . 

 O. C. Charlton. 



Besides Orthopsis occidentalis, nob., this is the only rep- 

 resentative ot the section of Diadematidce with perforated 

 and non-crenulated tubercles known from North American 

 rocks. 



Although a single recent species of Hemipedina is known 

 (H. cubensis, A. Ag. ), this genus is known as a fossil, from 

 Jurassic and lower Cretaceous rocks only; and its occurrence 

 in the upper part of the Washita division therefore confirms 

 the conclusion which the writer has previously drawn from 

 the similar occurrence of Holecfypus, that the Washita 

 division should be referred to an epoch not later than late 

 Neocomian.* 



Pecten inconspicuus, sp. nov. 



Shell small, thin, subcircular, a trifle higher than k)ng, 

 slightly truncated anteriorly and posteriorly, right valve 

 gently convex, its outer surface smooth except for faint con- 

 centric strife and a few remote, subimbricate growth-lines; 

 umbonal angle sharp at apex, nearly a right angle; anterior 

 ear (imperfect in the type) reentrant below, as indicated by 

 the direction of the stria? upon it, outline of posterior ear 



*See " Contribution to the Invertebrate Paleontology of the Texas Cretaceous," 

 in the Fourth Annual Report of the Geological Survey of Texas, Part II, p. 159. 



