796 CAMBRIAN BEACHIOPODA. 



The description of the type species gives all that is known of the genus. It differs from 

 Strophomena in ha\T.ng the cardinal process in the dorsal valve merged into a ridge formed by 

 the extension of the crural plates along the posterior margin so as to cover the delthyrium and 

 unite at the median line. 



Ty2)e. — StropTiomena (EostropJiomena) elegantula Walcott. 



Olservations. — The cardinal process is more like that of Orihoihetes than that of Strophomena; 

 it differs from both in being more simple in its construction. It is probable that there is a 

 group of shells having the characters of EostropTiomena elegantula (Walcott) , but owing to the 

 difficulty of obtaining interiors of the valves, it is impossible to designate them. Strophomena 

 aurora Billings [1865a, p. 218] is one of these; also, Leptaena decipiens [BilHngs, 1862c, p. 74]. 



EOSTEOPHOMENA ELEGANTXJLA (Walcott) . 

 Plate XCV, figures 6, 6a-b. 



Strophomena (Eostrophomena) elegantula Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 256-257. (Described 

 and discussed as below as a new species.) 



Strophomena (Eostrophomena) walcotti Moberg and Segekberg, 1906, Medd. fran Lunds Geol. Faltklubb, Ser. B, 

 No. 2 (Aftryck ur K. Fysiografiska Sallskapets Handl., N. P., Bd. 17), p. 71, PI. II, figs. 6, 6a-b ; PI. Ill, fig. 16?. 

 (Described and discussed in Swedish. The specific name "walcotti" is proposed because of the preoccupation 

 of "elegantula." The generic value now assigned to Eostrophomena permits the use of "elegantula." Figs. 6, 

 6a-b, in common with the remaining figures on PI. II of Moberg and Segerberg's paper, were copied from a 

 preliminary photograph of PI. XCV of this monograph.) 



General form transversely subsemicircular or subelliptical, greatest width at the straight 

 hinge line. Surface concavo-convex and marked by fine, radiating, even strire, separated into 

 flat bands by stronger and more prominent strise or ribs; fine concentric striae, and more or 

 less prominent lines of growth cross the radiating strias. The ventral valve is slightly convex, 

 with low umbo and small, incurved apex. The dorsal valve is flattened in the umbonal region 

 and concave toward the margins; the interior shows a narrow, rounded median furrow, also 

 rounded crural plates that unite with the cardinal process to form a continuous ridge covering, 

 the anterior portion of the delthyrium; the dental sockets appear to have been relatively large 

 and deep ; the adductor muscle scars are a httle to the front, as shown in figure 6b. 



A ventral valve 6 mm. wide has a length of 4 mm., and a dorsal valve 5.5 mm. wide is 

 3 mm. in length. 



Ohservations. — The concavo-convex shells and the ridge representing the cardinal process 

 place this little shell with the strophomenoid forms, but as no described genus possesses the 

 characters shown a genus is made to receive it. 



Formation and locality.— Passage beds between the Upper Cambrian and the Ordovician: (310j) Ceratopyge 

 limestone, at Borgholm; (310 [Moberg and Segerberg, 1906, description of PL III]) Ceratopyge limestone (Zone 4) at 

 Ottenby; and (390e [Moberg and Segerberg, 1906, pp. 71 and 109]) "Apatocephalus zone of the Ceratopyge suite," at 

 Ottenby; all on Oeland Island, Sweden. 



Superfamily PENTAMERACEA Schuchert. 



Family SYNTROPHIID^ Scliucliert. 



Genus SWANTONIA Walcott. « 



Swant07iia Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 296. (Mentioned as below as a new genus.) 

 Swantonia Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PL XI, and pp. 142 and 148. (Classification of 

 genus.) 



The description of the type species includes that of the genus, as there is only one other 

 species now referred to the genus, and that is very imperfectly known. 



a Prior to the definition ot the genus Swantonia the species now placed under that genus were referred to the following genera: 

 Camerella Billings [ISC.lb.p. 10; 1861c, p. 949; 1862e, | Camarella ? Hall and Clarke [1893, p. 220]. 



p. 221; 1863, p. 284). Protmhyncha? Schuchert [1897, p. 334). 



Camarella, Walcott [1886b, p. 122; lS91a, p. 613]. I 



