BILLINGSELLID^. 763 



are also in the dorsal valve the anterior adductor imi^ressions, as shown in figure 2k. In the 

 interior of the dorsal valve the deltidial cavity separates a small cardinal process or callosity, 

 which is straight (fig. 21) or subtriangular (fig. 2k). The crura are relativelj' long and very 

 prominent, with distinctlj^ defined dental sockets beside them. 



Ohservations. — This species was well illustrated by Barrande [lS79a, PI. LXII, fig. ii], and 

 I have copied five of his figures of a specimen showing the two valves united. In the material 

 of the collections of the Museum of Comparative Zoology, Cambridge, Massachusetts, there is 

 a fine series, illustrating the interior of the ventral and dorsal valves, that, through the kindness 

 of Dr. Alexander Agassiz, I was enabled to study and illustrate. 



The species in its external and internal shape varies so decidedly from all described forms 

 that it is not necessary to point out differences between them. 



The specific name was given in honor of Dr. Carl Rominger. 



Formation and locality.— Middle Cambrian: (345 [Pompeckj, 1896b, p. 509]) " Greenish shale in the Paradox- 

 ides zone, on the DlouhA Hora, above the brook of Sbirov, near Skrej ; (345c) "■ in shales of Etage C at Mleschitz; (345f) 

 in Etage C [Barrande, 1819a, PI. LXII], near Skrej; (345g) in Etage C [Barrande, lS79a, PL LXII], at Praschno Augezd; 

 (3451)<J shales of Etage Cat Jinec; and (345h) in Etage C [Barrande, 1879a, PL LXII], at Slap; all in Bohemia, Austria- 

 Hungary. 



BiLLINGSELLA SALEMENSIS (Walcott). 

 Plate LXXXVII, figures 3, 3a. 



Orthis salemensis Walcott, 1887, Am. Jour. ScL, 3d ser., vol. 34, pp. 190-191, PL I, figs. 17 and 17a. (Described and 

 discussed as below as a new species. The specimens represented by figs. 17 and 17a are redrawn in this mono- 

 graph, PL LXXXVII, "figs. 3 and 3a, respectively.) 



Orthis salemensis Walcott, Oehleet, 1889, Annuaire g^ologique universel for 1888, tome 5, 1889, p. 1139. (Described 

 in French.) 



Orthis salemensis Walcott, 1891, Tenth Ann. Kept. U. o. Geol. Survey, pp. 612-613, PL LXXII, figs. 6 and 6a. (The 

 text and figures are copied from Walcott, 1887, pp. 190-191, PL I, figs. 17 and 17a, respectively.) 



Billingsella salemensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 245. (Text copied from Walcott, 1887, pp. 

 190-191.) 



Shell about the average size of the Cambrian species of the genus. Transversely subquad- 

 rilateral; front broadly rounded and slightly sinuate midway; hinge line as long as the greatest 

 width of the shell. 



Ventral valve convex, most elevated about one-fourth the distance from the beak to the 

 anterior margin; beak small and incurved to the margin of the medium-sized area; the surface 

 of the area and the foramen have not been observed; mesial sinus broad and shallow, it is 

 marked by a low median rib and laterally by two costse on each side, a third appearing just 

 outside the sinus. 



The dorsal valve, associated in the same hand specimen of limestone, is slightly more 

 convex; frontal margin with a rather deep sinuosity to receive the projection of the ventral 

 valve; median fold broad and but slightly elevated, marked by two or three low costse; the 

 beak appears in the broken specimen in the collection to be scarcely elevated above the surface 

 of the shell, and to terminate at the cardinal margin; area imknown. 



The surface of both valves is marked by fine concentric lines of growth, and low, rounded 

 costse, varying in number from six or seven, as in the specimens figured, to twelve to fourteen 

 in other specimens. 



In the broad costse and the general aspect of the shell this species is un_ike any known to 

 me from the Cambrian, mth the exception of Billingsella whitfieldi (Walcott), from which, 

 however, it differs in strength and character of costse and outline of valves. 



The specific name is derived from Salem, New York. 



Formation and locality. — Lower Cambrian: (319b) Conglomeratic limestones at St. Simon; and (319h) lime- 

 stone bowlders in conglomerate at Metis on the St. Lawrence below Quebec; both in the Province of Quebec, Canada. 



a These localities arc represented in the collections of the United States National Museum. 



