50 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



supported by a prominent callosity or swelling in the 

 notothyrial cavity (the pseudocruralium of Walcott), 

 which is extended forward no farther than the middle 

 of the valve as a low axial thickening. Articulation 

 is accomplished by the sloping inner surface of the 

 ventral tooth which rests on the slanting outer surface 

 of the brachiophore. The cardinal process is a simple 

 linear ridge, a septum between the diductor muscles, 

 and serving also partly for muscle attachment ; but the 

 chief seat of attachment appears to have been on the 

 notothyrial callosity. 



The dorsal musculature of Billingsella is rather 

 obscure, but there appear to be four adductor impres- 

 sions, the posterior pair being located in the pits imme- 

 diately anterior to the notothyrial platform and being 

 somewhat larger than the anterior pair. 



Family EOORTHID^ Schuchert and Cooper 

 1931 



Orthacea wholly without deltidia and chilidia, so 

 far as known, and with or without a cardinal process. 

 Though not yet well understood, the family is now 

 considered to embrace the following genera: 



Wimanella Walcott 



Eoorthis Walcott 



Otusia Walcott 



Bohemiella Schuchert and Cooper 



Oligomys Schuchert and Cooper 



The genetic lines are thought to be about as shown 

 in Table 2. 



Table 2 



Otusia 



Eoorthis 



Oligomys 



Wimanella 



Bohemiella 



NiSUSIIDiE 



Unfortunately most of the species of the Eoorthidae 

 are not well understood internally, due to their poor 

 preservation or to lack of material. Nearly all of the 

 specimens come from limestone and accordingly most 

 of them are exfoliated, and but rarely are the interiors 

 of the valves nicely weathered out, as is so commonly 



the case with many of the brachiopods of the Ordovician 

 and later periods. Finally, we know the American 

 shells best, and the European and Chinese species are 

 regretfully few in number. On the other hand, the 

 brachiopods of the American Lower Ordovician 

 (Canadian) are almost unknown, and here are to be 

 expected the connecting links between the genera of 

 the Cambrian and the later Ordovician. Under these 

 circumstances a final classification of the Eoorthidae 

 along well determined genetic lines is yet to come, and 

 when it does, the phyletic lines into the Orthids and 

 Clitambonitida2 will be better established. 



Genus WIMANELLA Walcott 1908 



Walcott, Smiths. Misc. Coll., vol. 53, 1908, p. 98, pi. 10, 

 fig. 2; Camb. Brach., 1912, p. 745, pi. 89, figs. 2-2e, 

 t. fig. 64; Smiths. Misc. Coll., vol. 67, 1924, pi. 1 1 1, 

 figs. 2-4. 



Genoholotype. — Wimanella simplex Walcott 

 1908, an almost characterless species. Our presenta- 

 tion is based on the genotype and Billingsella (== 

 Wimanella) highlandensis (Wale). 



Description. Exterior. — Thin-shelled. Outline 

 subquadrate to subsemicircular; hinge-line straight; 

 cardinal extremities obtusely or acutely angular; lateral 

 profile subequally biconvex; ventral interarea longer 

 than dorsal; delthyrium open; notothyrium narrow, 

 open. Surface covered by fine concentric growth-lines 

 and obscure costellas. 



Ventral interior. — Delthyrial cavity shallow, diduc- 

 tor scars large, tapering anteriorly, separated dorsally 

 by a low ridge, which forks anteriorly about the adduc- 

 tor impression; pallial trunks prominent. 



Dorsal interior. — Crural plates short; axial ridge 

 low, extending forward to about the middle of the 

 valve. Cardinal process apparently absent. 



Geologic range. — Lower and Middle Cambrian 

 of North America. 



Species 



Orthis ? highlandensis Walcott 1886 

 Wimanella ? anomda'W Aeon 1905 

 W. borealis Walcott 1924 

 W. Shelby ensisWilcoXl \9Q^ 

 W. simflex Walcott 1908 



Distinguishing characters. — The name Wim- 

 anella may serve for Lower and Middle Cambrian 

 nearly smooth or very finely ribbed billingsellids of the 

 type of W. simplex Walcott. As stated by Walcott 

 (1912), the genus was to embrace the older and 

 smooth shells of the Billingsellidse, but a study of all 

 of his species of Wimanella at the U. S. National 

 Museum shows the presence of faint radiating lines in 

 shells conspecific with the genotype and in the actual 

 types. Obviously, then, the characterization of this 



