BILLINGSELLID^. 761 



of the ventral valve shows the presence of a tripartite, elevated umbonal space into which 

 the strong main vascular sinuses extend, as in BillingseUa coloradoensis (Shumard); the 

 sinuses extend forward nearly to the front margin of the valve. Of the interior of the dorsal 

 valve only the presence of a strong median ridge is known. 



Ohservations. — This species is one of the costate species of the type of Billingsella colorado- 

 ensis (Shumard) and B. romingeri (Barrande). It differs from them in surface characters. 

 It may be considered the trans-Pacific representative of B. coloradoensis. 



The specific name was given in honor of Raphael Pumpelly. 



Formation and locality. — Upper Cambrian: (C36) Upper part of the Chaumitien limestone [Blackwelder, 

 1907a, p. 36 (part of 3d. list of fossils), and fig. 9 (bed 2), p. 35], at Chaumitien, Changhia district; and (C61) a dense 

 Hack limestone in the uppermost limestone member of the Kiulung group {Blackwelder, 1907a, pp. 37 and 41 {3d list of 

 fossils)and fig . 10 {bed 13), p. 5S], 3 miles {4.8 km.) southwest of Yenchuang; both in Shantung, China. 



^ Billingsella eetroflexa (Matthew). 

 Plate XC, figm'es 1, la-h. 



Not Gonambonites plana retroflexa db Verneuil [Pander, 1830, Beitrage zur Geognosie des russischen Reiches, p. 77, 



PI. XXV, figs. 1 and 2]. 

 Clitambonites {Gonambonites) plana retroflexa Matthew, 1895, Trans. Roy. Soc. Canada for 1895, 2d ser., vol. 1, sec. 4, 



No. 13, p. 267, PI. II, figs. la-c. (Original description of Gotmmbonites plana retroflexa by de Verneuil [Pander, 



1830, p. 77] copied and variety from Cape Breton described and discussed. The specimens represented by 



flgiues la and lb are redrawn in this monograph, PI. XC, figs. Ig and If, respectively.) 

 Clitambonites planus retroflexus (Matthew), Schuchert, 1897, Bull. U. S. Geol. Survey No. 87, p. 184. (Merely changes 



generic reference.) 

 Billingsella retroflexa Matthew, 1903, Geol.-Survey Canada, Rept. Cambrian Rocks Cape Breton, pp. 148-151, PI. 



X, figs. 2a-e. (Described and discussed. Figs. 2a, 2c, and 2e are copied fi-om Matthew, 1895b, PL II, figs. 



la-c, respectively. The specimens represented by figs. 2a, 2c, and 2d are redrawn in this monograph, PI. LX, 



figs. Ig, If, and Ic, respectively.) 

 Orthis (PlectortMs) retroflexa (Matthew), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 270-271. (Characterized 



and discussed essentially as below.) 



This species is distinguished by the fine radiating costse on the ventral valve (PL XC, 

 figs. 1, la-c) and coarser costee on the dorsal (fig. If). The fine longitudinal strige on the 

 costse are sho\vn by figure le. The latter are similar to those of Eoorthis remnicha (PI. XCII 

 fig. 2c). All that could be definitely determined of the interior of the valves in the type 

 material sent me by Matthew is shown by figures If, Ig, and Ih. In figure Ig of the ventral 

 valve the casts of the pseudospondyHum, area, and base of the main vascular sinuses are 

 shown. In figure If of the dorsal valve the casts of the strong cardinal process, dental sockets, 

 and crura are shown, and in figure Ih the ovarian areas and the visceral area between them. 

 Matthew [1903, p. 148] describes other features of the interior of the valves. 



The character of the costse and general features of this shell, as far as known, appear to 

 class it with Billingsella romingeri (Barrande) (PI. XC) and B. coloradoensis (Shumard) (PI. 

 LXXXV). 



Matthew's very full description [Matthew, 1903, pp. 148-151] should be read by the 

 student of this species. By inadvertence [Walcott, 1905a, p. 270] I referred it to OrtJiis (Plec- 

 tortMs), a name wliich I was then using to include those forms which are now placed under 

 Eoorthis. 



Formation and locality. — Uiddle Cambrian: (307d [Matthew, 1903, p. 149]) Sandy limestone of Matthew's 

 [1903, p. 19] Etcheminian, on Young (McFees) Point, near George River, Cape Breton, Nova Scotia. 



Billingsella richthofeni Walcott. 



Plate LXXXIX, figure 1. 



Billingsella richthofeni Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 242-243. (Characterized and discussed as 

 below as a ne-w species. ) 



This species is represented by two specimens of the exterior of the ventral valve measuring 

 4 and 5 mm., respectively, in length and width, these being about the same. The outer sur- 

 face is marked by fine, obscure, radiating ribs and very fine concentric strise. The general 



