NATURAL SCIENCES OF PHILADELPHIA. 5 



median septum a low ridge appearing a short distance from the beak, and 

 disappearing toward the middle of the valve; vascular imprints sectoriform 

 reaching half way to the midvalve, separated from the median septum bj a 

 faint ridge (occlusor apophysis ?) on each side. External surface of both 

 valves with numerous concentric lamellar striae and innumerable little pits 

 which give the impression a finely granular appearance ; pits more scattered 

 and deeper toward the anterior margin. Internal surface (of dorsal valve) 

 exhibiting concentric lines and innumerable raised points, apparently corres- 

 ponding with the pits of the exterior. 



Length -82(100); width 1-06(129); length of hinge-line -55(67); length of 

 cardinal process -04 (5) ; depression of dorsal valve -04 (5). Depth of ventral 

 valve -15, with a length of -76. Another dorsal valve has a width of 1-46 and a 

 hinge-line 1-22 long. 



Tttis anomalous species has more the form of an Orthis or Strophalosia than 

 a Producta. But there is no positive proof of the existence of spines, and the 

 somewhat doubtful existence of an area in either valve furnishes only unsatis- 

 factory grounds for referring it to either genus. At the same time it is difficult 

 to understand how the externally projecting cardinal processes of the dorsal 

 valve could be used without a fissure (and area?) in the ventral valve in which 

 they could move. In view of all the facts, I venture to refer the species with a 

 query to Strophalosia. Should the reference prove correct, it will be, so far as 

 1 know, the first identification of this genu3 in American rocks. 



CH0XETE3, Fischer. 



Chonetes mdlticosta, n. sp. Shell of medium size or larger, semicircular, 

 with the greatest width along the hinge-line. Ventral valve depressed-ventri- 

 cose, more or less flattened toward the hinge extremities ; with a barely per- 

 ceptible mesial sinus reaching two-thirds the distance to the flattened incon- 

 spicuous beak; spines two (possibly three) each side of the beak, nearly at 

 right angles with the hinge-line, of medium length, rather stout, the first mid- 

 way between the beak and cardiual extremity, the second midway between this 

 and the same point; area extremely narrow. Dorsal valve shallow, concave, 

 with a depressed mesial fold extending nearly to the beak ; socket plates very 

 divergent ; occlusor scars forming a very small elleptic pit near the beak. Ex- 

 ternal surface of each valve bearing 180-200 fine, subflexuous, radiating stria?, 

 which increase dichotomously at all distances from the beak, and some:imes 

 also by implantation. Surface of cast rather remotely punctate. 



Length of hinge-line -82 (100) ; length of shell -50 (61); convexity of ven- 

 tral valve -12 (14). In most specimens the last measure is relatively less. 



Ranges from the base of the yellow sandstones into the base of the Burling- 

 ton limestone. Intermediate in size between C. Logani and C. Fischeri of Nor- 

 wood and Pratten. It possesses a greater number of radiating striae than C. 

 lllinoiensis of Worthen . 



Chonetes Illinoiensis, Worthen, (Trans. St. Louis Acad. Nat. Sci., i. 571 ;) 

 C. Logani, Hall, (Iowa Rep. p. 598, pi. xii. fig. 1, a-e and 2,) not C. Logani, Nor- 

 wood and Pratten, (Jour. Acad. Nat. Sci. Philada., [2] iii., p. 30, pi. ii. fig. 12, 

 a, b, c.) 



Some confusion seems to exist among the species of Chonetes just mentioned. 

 C. Logani was described "from the middle portion of the mountain limestone 

 series," at Burlington, Iowa, and characterized as having "about 30 rugose 

 ribs."/ The figure agrees with the description. Prof. Hall subsequently 

 described a species from the Burlington limestone, of Burlington and Quincy, 

 which he referred to C. Logani, Nor. and Prat., though, among the characters, he 

 assigns to it " 100-120 or more fine rounded dichotomizing striae." Still later, 

 Mr. Worthen, conceiving this form to be specifically distinct, gave it the name of 

 C. lllinoiensis, remarking that it " is restricted to the crinoidal beds of the 



1863.] 



