640 CAMBEIAN BEACHIOPODA. 



The subcentral position of the apex seems to distinguish this species. It is associated 

 with Oholus {Broggeria) salteri (Holl) and Lingulella lepis (Salter) . 

 The specific name is derived from Borgliolm, the type locaHty. 

 FoEMATiON AND LOCALITY. — Tipper Cambrian: (310d) Ceratopyge slate at Borgholm, Oeland Island, Sweden. 



ACEOTHELE CERATOPYGARUM (BrOggCr) . 

 Plate LXIII, figures 1, la-c. 



Discina (Acrotretaf) ceratopygarum Brogger, 1882, Die siliirischen Etagen 2 und 3, p. 47, PI. X, figs. 1, la-b. (De- 

 scribed in German. Figs, la and lb are reproduced in this monograph, PI. LXIII, figs. 1 and la, respectively.) 



Acrothele ceratopygonum Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, p. 598. (Mentioned in discussion of Acrotreta 

 seebachi.) 



Acrothele ceratopygarum (Brogger), Mobeeg and Segeebbrg, 1906, Medd. fran Lunds Geol. Faltklubb, Ser. B, No. 2 

 (Aitryck ur K. Fysiografiska Sallskapets Handl., N. F., Bd. 17), p. 67. (Mentioned in Swedish.) 



Acrothele barbata Moberg and Segerbbeg, 1906, idem, pp. 67-68, PI. Ill, figs. 7-10. (Described and discussed in 

 Swedish as a new species.) 



Ventral valve conical, with eccentric apex. False area well defined and marked midway 

 by a narrow, slightly elevated ridge that does not extend quite to the margin of the shell; on 

 the interior of the shell a narrow furrow extends nearly to the margin where it is cut off by 

 a transverse ridge just witliin the margin. Foraminal aperture minute, situated at the top 

 of the false area just below the apex; in the exfoliated shell it appears to be elongate. The 

 outer surface of the shell appears in a cast to be nearly smooth; the inner layers or lamellae 

 are marked by fine concentric and radiating lines. A cast of the interior shows a very small 

 visceral area just in front of the apex, and a cardinal muscle scar on each side of the median 

 line back of the cast of the foraminal opening. The two ventral valves measure 5 mm. in 

 diameter; height, about 2 mm. 



From Moberg and Segerberg's description [1906, p. 67] of the dorsal valve of Acrothele 

 'barbata the following is taken: "The dorsal valve is nearly flat, or with the posterior and cen- 

 tral parts slightly arched; beak marginal." The interior shows a few traces of muscle scars. 

 The interior of the ventral valve shows the main vascular sinuses and branches very much as 

 in Acrothele coriacea Linnarsson (PI. LVI, figs, la. Id). These authors give the dimensions 

 of one of the larger shells as, length, 5.25 mm.; width, 6 mm.; elevation, 1.5 mm. 



Observations. — Through the courtesy of Doctor Brogger I have had the opportunity of 



studying the type specimens of this species. One of them is illustrated (PL LXIII, fig. Ic), 



and I have also copied two of Brogger's figures. The species is related to Acrothele borghol 



. mensis Walcott from the Ceratopyge slate, but differs in the character of the false area and 



median ridge of the latter. It is also a larger and more convex form. 



Specimens from Vestfossen, Norway, one of which is illustrated on Plate LXIII, figure lb, 

 have the same form as the shells described by Moberg and Segerberg under the name of Acro- 

 thele barbata [1906, p. 67], and I find bits of the outer shell showing the "coarse, irregular, 

 anastomosing, concentric ridges" characteristic of Acrothele barbata; a little trace of the marginal 

 fringe is also shown on one specimen. The fact that the two species occur at the same strati- 

 graphic horizon in Sweden and Norway, and the fact that they have the same specific characters, 

 lead me to place A. barbata as a synonym of Brogger's A. ceratopygarum. 



This species derives its specific name from its occurrence in the Ceratopyge limestone. 

 Formation and locality. — Passage beds between the Upper Cambrian and the Ordovician: (3231i [Brogger, 

 1882, p. njj blue Ceratopyge limestone, at Vestfossen, 10 miles (16.1 1cm.) west-southwest of Christiania, Norway. 

 (310 [Moberg and Segerberg, 1906, p. 67]) Ceratopyge limestone (zone 4), at Ottenby, on Oeland Island, Sweden. 



[ Acrothele colleni n. sp. 



Text figures 55A-E, page 641; Plate LXIII, figures 6, 6a-b. 



This species is represented by numerous specimens of both valves, but only the exterior 

 of the valves is known. The ventral valve is subcorneal, with the apex a little in front of the 



