Bkede.] Carboniferous Invertebrates. 115 



with rather depressed or flattened irregular radiating cos tee, of 

 which only about twelve or fourteen of the largest reach the 

 beak, others dying out at various distances between the mar- 

 gins and the umbo; in proportion to size, the larger of the 

 intercalated ones being longer than the smaller. Crossing all 

 of these are numerous fine concentric striae, some of which on 

 the ears, particularly the anterior one, often form little vaulted 

 scales ; in well-preserved specimens these vaulted projections 

 are strongly developed on one of the posterior cosfoe of the body 

 part of the valve. Surface of right valve generally with only 

 very obscure radiating costse and fine crowded lines of growth." 

 Measurements : Length, 24 mm. ; height, 26 mm. ; convexity, 

 about 5 mm. 



Range and distribution : Upper Coal Measures ; Turner, 

 Eudora, Lawrence, Topeka, Wabaunsee county. 



Aviculopecten rectilaterarius. 



Avicula rectUateraria Cox, Geol. Surv. Ky., in, p. 578, p. ix, f. 2, (1857). 

 Avfrvfopecten rectilaterarius Meek and Worthen, Geol. Surv. 111., n, p. 

 326, (1866). 



Shell variable in outline, about as long as high ; ventral mar- 

 gin rounded, nearly semicircular; posterior margin nearly 

 straight, meeting the hinge at nearly a right angle ; anterior 

 margin slightly sinuate at the lower part of the ear, then, round- 

 ing upward, meets the hinge line ; lower anterior margin more 

 abruptly rounded than the corresponding posterior one ; hinge 

 line slightly shorter than the shell, the beak not extending 

 above the hinge ; posterior ear not separated from the shell by 

 a sulcus, anterior ear separated from it by an indistinct furrow. 

 The anterior ear of the right valve contains a sharp byssal 

 notch. The shell is marked by fairly prominent, slightly sinu- 

 ous, radiating striae, which increase by implanation and bifur- 

 cation ; on the posterior ear of the left valve these striae are 

 very dimly visible but are more prominent on the anterior ear. 

 These stria* are crossed by very fine, close, concentric stria 1 and 

 larger lines of growth. Measurements, two specimens : Length, 

 18 mm., 18 mm. ; height, 19 mm., 15 mm. 



