632 CAMBEIAN BEACHIOPODA. 



margin (PL LX, fig. Ik), but larger scars occur and extend farther forward into the valve (PI. 

 LXII, fig. If; PI. LVIII, figs. 3c, 3d, and 5h). The central and anterior lateral scars are 

 situated essentially as in Obolus; the former on the slopes of the median ridge and the latter 

 at the anterior end of the ridge. 



Type. — Acrothele coriacea Linnarsson. 



Observations. — The generic description is drawn up from the material studied in connec- 

 tion with the various species now referred to the genus. One of Linnarsson's species, Acrothele 

 granulata [1876, p. 24] I have taken as the type of the subgenus Redlichella on account of the 

 differences in the interiors of the valves. 



Surface cJiaracters. — The surface characters of the various species of Aaroihele vary nearly 

 as much as those of Micromitra. The species may be grouped by the surface features under 

 three headings: (1) Striato-granulose; (2) concentrically ridged, striated, or nearly smooth; 

 (3) pseudopunctate. 



The fii-st group, striato-granulose or radulo-granulose, includes, as now known, sixteen 

 species and seven varieties. The surface of the type species of the genus, Acrothele coriacea 

 Linnarsson, is representative of this form of surface. It has concentric lines of growth, and 

 a series of concentric, irregular, more or less inosculating, rounded, fine ridges upon which 

 minute nodes or granules occur; these granules, on some species, are more or less regularly 

 arranged on the ridges and appear over nearly the entire surface (PL LVI, fig. Ig), while in 

 others they are scattered irregularly (PL LXI, fig. 4d). On Acrothele matthewi (Hartt) (PL 

 LXI) and some other species the younger shells are granulated, while on the older shells the 

 ridges are fahly regular and only an occasional granule occurs on them. On most adult shells 

 with this form of surface the ridges near the margin are more regular and rarely inosculate. 

 This type of surface occurs also on Acrothele (Redlichella) granulata (Linnarsson) (PL LVI, 

 fig. 2g) and Botsfordia granulata (Redlich) (PL LVII, fig. 4r) and Botsfordia cselata (Hall) 

 (PLLIX, figs. Ihand lo). 



The species upon which I have seen the ridges and granules are: 



Acrothele avia Matthew. 



avia puteis Matthew, 

 bergeroni Walcott. 

 colleni Walcott. 

 coriacea Linnarsson. 

 decipiens Walcott. 

 gamagei (Hobbs). 

 intermedia Linnarsson. 

 matthewi (Hartt). 

 matthewi eryx Walcott. 

 - matthewi lata Matthew, 

 matthewi mxilticostata Matthew. 



Acrothele heUula Walcott has this type of surface, but the ridges and granules are so minute 

 that they are only to be seen with a very strong lens. 



The second group is concentrically ridged, striated, or smooth, as far as known. I think, 

 however, that with better-preserved specimens some of the species now included under it would 

 be found to have the striato-granulose surface. 



The species referred to it are: 



Acrothele bohemica (Barrande). Acrothele? minuta Walcott. 



borgholmensis Walcott. Acrothele nitida (Ford), 

 ceratopygarum (Brogger). turneri Walcott. 



levisensia Walcott. woodworthi Walcott. 



maculata (Salter). 



On the pseudopunctate surface the union of the inosculating ridges is very regular 

 and the hollows or pits between the ridges are arranged in oblique lines that appear to start 

 on the posterolateral margins of the valves and curve obliquely forward to the opposite 



Acrothele panderi Walcott. 

 pretiosa (Billings), 

 prima (Matthew), 

 prima costata (Matthew), 

 proles Matthew, 

 quadrilineata Pompeckj. 

 spurri Walcott. 

 subsidua (White), 

 subsidua hera Walcott. 

 subsidua Ifevis Walcott. 

 yorkensis Walcott. 



