33b PALAEONTOLOGY OF ILLINOIS. 



ceus, forms so nearly resembling our shell as to strengthen the suspicion that 

 they may all belong to one species. His fig. lab, pi. xv, representing a right 

 and left valve of P. pusillus, agree very nearly with those before us, excepting 

 that his fig. 1 a represents the left valve as having distinct radiating markings 

 on the anterior ear ; while his figures of both valves show the beaks a little 

 more prominent. His figures 2 ab and 3 a b, representing right valves of 

 larger individuals, figured under the name P. sericeus=(Avicida sericea, de Ver- 

 neuil), which he regards as identical with P. pusillus (sp.), Schlot.,* agree well 

 with the corresponding valve of our shell, except in having the anterior ear 

 narrower, and the sinus under it wider. On plate xix, fig. 23, he gives a figure 

 of a left valve, under the name P. sericeus, that shows, though in a less marked 

 degree than some of our specimens, the peculiar backward obliquity that leads 

 us to think these forms may belong to Strebloptcria. 



In making comparisons with our figure 9 a, the reader should be informed 

 that the engraver has shaded the posterior ear so as to look too abruptly flat- 

 tened and distinct from the umbonal region, while the concentric strias should 

 only be barely indicated, and closely crowded, instead of rather distinctly visi- 

 ble and distant. Some of the specimens have the anterior margin much 

 more prominently rounded than that we have figured, so as to give a greater 

 backward obliquity to the whole outline.. This is particularly the case with 

 left valves, in which the anterior oblique umbonal slope is quite distinct from 

 the flattened anterior ear. 



Locality and 'position : South line of Clinton county, Illinois; Upper Coal 

 Measures, near No. 11 coal; associated with Monopteria longispina, (Gervillia 

 Cox), Myalina Swallovi, McChesney, and a large Myalina, agreeing with a 

 form figured by Meek and Hayden, in their Upper Missouri Palaeontology, p. 

 33, as M. subquadrata, Shumard, var. ampla. 



Genus EUMICKOTIS, Meek. v 



Synon. — Avicula (sp.), Auct., (not Klein.) 



Monotis, King, 1849; Meek & Hayden, 1858; Shumard, 1859; (not Bronn, 1830). 

 Aucella, McCoy, 1852. Brit. Paleozoic Foss., p. 481 ; (notKeyserling, 1842). 

 Eumicrotis, Meek, March, 1864. Am. Jour. Sci., xxxvii, p. 216; Palaeontology 

 Upper Missouri, 1865, p. 53. 



Shell suborbicular, plano-convex, the left valve being usually 

 very convex and the right flat, or even a little concave ; not 



* We should have little hesitation in referring the shells figured by Dr. Geinitz, to 

 P. pusillus, but judging from deVerneuil's single figure of his Avicula sericea, we 

 should, like that gentleman, have regarded it as an entirely distinct species. 



s . / v. J. ■£•/*■ 



C. O 



