NATURAL SCIENCES OP PHILADELPHIA. 113 



to greatest width of shell ; mesial sinus wanting or barely perceptible ; exter- 

 nal surface marked by fine, rigid, sharp, once dichotomizing radial lines or 

 ribs, numbering about 40. No indications of spines have been detected. 



Length of hinge line, "29 (100) ; length from beak to anterior margin, 

 21 (72). 



Described from an imperfect ventral valve ; but its peculiar characters 

 easily distinguish it. 



Museum of University of Michigan, Collected by A. Winchell at Valley 

 Forge, one and a half miles below Cuyahoga Falls, Ohio. 



PfiODtjcTA duplicostata, n. sp. Shell rather large with subcircular outline. 

 Ventral valve very ventricose and greatly arched, with steep slopes to the 

 right and left margins, not enlarged at the aperture, and entirely destitute of 

 mesial sinus ; marked with numerous interruptedly and irregularly striate 

 sinuous ribs, which dichotomize once or twice in the middle region of the 

 valve, and towards the front resolve themselves each into a fascicule of three 

 or four smaller ribs, themselves raised into a wider rib-like elevation around 

 the anterior margin. The tubular spines are scattered over the whole exte- 

 rior, but become much more abundant at the commencement of the marginal 

 costate ridges. The whole exterior of the cast is marked also by oblique 

 punctations, which are placed mostly in irregular lines between the ribs, and 

 become consequently most abundant toward the margin. On the sides of the 

 cast the punctations become elongated into short furrows which cross the 

 surface obliquely. 



Length, 1*19 ; breadth, 1*24; convexity of ventral valve, "58; number of 

 marginal ridges, 15 to 20. 



Collected by A. Winchell, at Battle Creek, Michigan. Occurs also in Lick- 

 ing County, Ohio. 



Producta morbilliana, n. sp. Shell smal', transversely subelliptic, only 

 moderately produced. Hinge line seven-eighths the greatest width of the 

 shell; ears small, nearly right angled. The shell regularly contracts from 

 the aperture to the beak, which is small, subacute, and projects slightly be- 

 yond the hinge. The arching of the shell is such that when resting on the 

 aperture the greatest height is equal to one-half the greatest width. No 

 sinus or flattening present. The surface is marked by a series of deep, con- 

 tinuous, equidistant wrinkles, ten or eleven in number, becoming obscure 

 toward the beak ; between the wrinkles are numerous fine concentric stris 

 not easily seen without a magnifier. These features are crossed by a longitu- 

 dinal system which, near the beak, is a set of fine regular costae, which near 

 the middle become interrupted by the wrinkles, and, losing their identity, 

 result in several concentric bands of short longitudinal tubes buried in the 

 substance of the shell, and gradually emerging and presenting their apertures 

 anteriorly. 



Transverse diameter of aperture, '58 (100) ; length of hinge line, -51 (88) ; 

 distance from hinge line across the aperture to opposite side, -44 (76) ; height 

 of shell when resting on the aperture, "26 (45). 



From the base of the Burlington limestone, Burlington, Iowa. "White 

 Collection " of the University of Michigan. 



A cast from the yellow sandstone below (probably "No. 5,") is probably 

 identical with this. 



This beautiful species is most nearly related to P. speciosa, Hall, (xth Rep. 

 N. Y. Reg. p. 176.) The resemblance, however, is not striking, except in 

 the cast referred to. This differs in having the pustules more regularly ar- 

 ranged in concentric bands. P. morbilliana may also be compared with P. 

 Rogersi, Nor. and Prat., (Jour. Acad. Nat. Sci. Phil. [2] iii. 9, pi. i. 3, a, b, 

 c, not P. aspera McChesney.) It is, however, a much neater species, without 

 trace of sinus, not so full near the beak, while the rib-like tubes arranged 

 1865.] 



