CUETICIIDiE. 369 



Dall tells me that he did not see Jeremejew's paper in which the specific name ladogensis was 

 proposed. 



Ten years later Karpinsky [1887, p. 476], in his report on the Geology of the Government 

 of Pskow, gives a list of the species occurring in the Ungulite sandstone and places a footnote 

 after the word Helmersenia, in which he refers to " Keyserlingia" and suggests that the species 

 be called "Keyserlingia panderi." In this footnote he mentions "Keyserlingia" three times, but 

 places after the first a reference to Pander's description of Helmersenia. It is evident that 

 Karpinsky intended to specifically identify panderi with Helmersenia and not Keyserlingia. 



A few months after the appearance of Karpinsky's paper Oelilert, in Fischer's Manuel de 

 Conchyliologie, describes the genus Helmersenia [1887, p. 1264] and gives as the type H. jeremejewi 

 Pander. He gives no reference, but it is likely that he followed Dall. 



This form owes its specific name to its occurrence near Ladoga, near St. Petersburg, Russia. 

 Formation and locality. — Upper Cambrian: (336o) Ungulite grit, Koporje, Government of St. Petersburg; 

 (336p) Ungulite grit, Kunitz, Government of Pskow; and (336ct [Jeremejew, 1856, pp. 73 and 80}) Ungulite sandstone, 

 near Ladoga, Government of St. Petersburg; all in Russia. 



SuperfamUy OBOLACEA Schuchert. 



Family CURTICIID.^ Waleott and Schucliert. 



Genus CTJBTICIA Waleott. 



Curtida Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 319. (Mentioned as below as a new genus.) 



Curticia Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 143. (Classification of genus.) 



The description of the type species, Curticia elegantula, includes all that is known of this 

 genus. 



The generic name is given in recognition of the excellent work of Dr. Cooper Curtice, of 

 Moravia, New York, both as a field collector and laboratory assistant. 



CXJRTICIA ELEGANTULA Walcott. 



Plate I, figures 2, 2a-l. 



Curticia elegantula Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 319-320. (Described and discussed as below as 

 a new species.) 



General form subcircular, biconvex. Surface of exterior of shell marked by fine, concentric, 

 slightly undulating strise, and lines and varices of growth. When the thi'n exterior layer is 

 exfoliated, the inner layers are ornamented by numerous fine, radiating lines, very much as 

 in Dicellomus and Oholus, also by more or less imbricating concentric lines. The inner surface 

 shows radiating and concentric lines without the visceral area. Shell substance corneous and 

 probably calcareous. The shell is built up of a thin, outer, surface layer and several inner 

 layers or lamellae, slightly oblique to the outer surface on the umbo and central parts of the 

 valves. The lamellae are more oblique and numerous toward the front and sides, and thus 

 thicken the shell over those parts. The average ventral valve has a length of 5 mm.; width, 

 6 mm. ; dorsal valve, 5 mm. by 5 mm. 



Ventral valve strongly convex, most elevated at the umbo, and arching over to a minute, 

 slightly incurved apex; area rudimentary, with a high, triangular, open delthyrium occupying 

 most of it. A cast of the interior of the valve shows that a narrow, elevated ridge occurs just 

 in advance of the apex, and a very small visceral area is indicated. 



Dorsal valve evenly convex, apex marginal; cardinal area rudimentary, narrow, and 

 divided by a low, broad, open delthyrium. The interior shows a median ridge and septum, 

 with small rounded depressions beneath the umbo on each side of the median ridge and a little 

 in advance of the apex. Ventral muscle scars small and clearly defined. Anterior lateral 

 scars small and situated in advance of the central scars close to the median ridge and at its 

 anterior extremity. Main vascular sinuses broad and slightly defined. 



Observations. — This shell was labeled by the field collector as Dicellomus politus. In 

 external form it resembles that species, but the open delthyrium of the ventral valve and the 

 62667°— VOL 51, pt 1—12 24 



