288 PALEONTOLOGY OF NEW YORK. 



The whole structure is very similar to the brachidium of the adult living 

 Magellania (Waldheimia).* 



The adductor scars are more or less distinct, the anterior members being the 

 more clearly defined. These scars are usually represented only by three straight 

 lines diverging from the umbonal region. Vascular sinuses originate about the 

 muscular areas of both valves and are directed forward with frequent rami- 

 fications. 



The shell-structure is highly punctate. 



It thus appears that the Devonian shells which can be referred to Crypto- 

 nella do not materially differ in the structure of the brachidium from the living 

 Magellania. There are several species in the American faunas, currently 

 referred to this genus, whose brachidia have not yet been developed, e. g., 

 C. eximia, Hall, of the Lower Helderberg, C. Iphis, Hall, of the Upper Helder- 

 berg, and C. Eudora, Hall, of the Chemung, but in all these the probability of 

 their being congeneric with C. rectirostra, is enhanced by the demonstration of 

 the absence of the transverse dorsal band on the brachidium of the latter. 

 From Davidson's determinations we know that the same type of brachidium 

 existed in the Devonian faunas of Great Britain, Waldheimia juvenis, Sowerby 

 (sp.), and W. Whidbornii, Davidson,! both shells with smooth exterior, the latter 

 with biconvex valves, the former with a plano-convex or centronellid contour. 

 From certain preparations made by Dr. Carl Rominger, in 1863,J it was deter- 

 mined that the Terebratula or Retzia melonica, Barrande, from the Bohemian 

 Etage Fj (Konieprusian), possesses a brachidium of the same type. This is a 

 large biconvex shell quite different in expression from the diminutive navicu- 



* In the description and illlustratioDS of 18ti7 the brachidium was represented as possessing a trans- 

 verae band on the dorsal side, uniting the descending branches at points just below, and slightly back of 

 the position of the crural apophyses. Such a transvei-se band does not exist. In making preparations 

 of these internal parts slight ineptitude will divide the long concave hinge-plate in such a manner that 

 ite anterior edge remains attached to the crura. Repeated attempts with the knife have almost invariably 

 given this result, but certain specimens in which the entire brachidium has been changed to pyrites 

 have determined the inaccuracy of such preparations and the absence of this abnormal structure. 



t Devonian Supplement, 1882, pp. 13, 13, pi. i, figs. 1-4. 



I Sixteenth Report on New York State Cabinet of Natural History, p. 49, figs. 24-26. See also Bar- 

 KAXOK, Systime Silurien, vol. v, pi. cxli. 1879. 



