52 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



are placed slightly outside the delthyrial margins. In 

 connection with the teeth there are receding dental 

 lamellae like those in Hesferorthis tricenaria. The 

 front ends of the dental plates are continued as a callus 

 around the margin of the muscle marks. The muscle 

 field is placed on a slight thickening as is seen com- 

 monly in H. tricenaria, but there is in the type species 

 no pseudospondylium such as occurs in Finkelnburgia. 

 The muscle area is similar to that in Billingsella in 

 plan but the adductor track is not so long as in that 

 senus. On the other hand, the shell of E. remnicha is 

 too thin and too strongly ribbed to preserve the mam 

 pallial sinuses. 



In none of the species studied and belonging to 

 Eoorthis was there seen a trace of a deltidium, and it is 

 therefore reasonable to suppose that none of the species 

 had one. 



The dorsal valve of the genotype is much like that 

 of Billingsella. The crural plates are flat, oblique, and 

 divergent. They are supported by adventitious deposit 

 which cements them to the valve and forms the noto- 

 thyrial platform, and the latter supports the crural 

 plates on their inner surfaces; the palintrope overlaps 

 them on the ventral surfaces. The sockets are deep 

 but very narrow, and the cardinal process is very low 

 and linear. The median ridge is low, widening toward 

 the front, and represents an elevation corresponding 

 to the dorsal sulcus. 



In the external forms of the valve and the internal 

 structures one sees readily a rather strong resemblance 

 between Eoorthis and the later Orthida. The dental 

 plates, muscle marks, and certain details of the cardinalia 

 of Eoorthis appear to bridge the structural gap between 

 the Cambrian brachiopods on the one hand and the 

 later orthids on the other. It is too early to state 

 definitely the possible course of these evolutional lines; 

 many of the genera of the Ozarkian and Lower 

 Ordovician (Canadian) are yet to be described. 



Genus OTUSIA Walcott 1905 



Wakott, Proc. U. 8. Nat. Mus., vol. 28, 1905, p. 246; 

 Camb. Brach., 1912, p. 769, pi. 93, figs. 4-4d. 



Genoholotype. — Orthis sandbergi Winchell 

 1886, Geol. Nat. Hist. Surv. Minn., 14th Ann. Rept., 

 p. 318, pi. 2, figs. 8, 9. 



Description. Exterior. — Shell small, transverse, 

 hinge-line straight, cardinal extremities acute, com- 

 monly mucronate; lateral profile biconvex; dorsal 

 valve provided with a prominent shallow sulcus, ventral 

 valve with a low fold. Ventral interarea moderately 

 apsacline; delthyrium wide, open. Dorsal interarea 

 anacline, notothyrium open. Surface multicostellate. 

 Test impunctate. 



Ventral interior. — ^Teeth strong, dental plates ob- 

 lique as in Billingsella. Muscle-scars not strongly 

 impressed. 



Dorsal interior. — Notothyrial cavity shallow, brachi- 

 ophores rudimentary as in Billingsella ; cardinal process 

 simple, a broad median ridge. 



Geologic range. — Upper Cambrian and possibly 

 also Middle Cambrian of North America. The only 

 species are O. sandbergi (N. H. Winchell) and O. 

 {?) utahensis Wslzott 1912. 



Distinguishing characters. — The diagnostic 

 generic characters of Otusia, according to Walcott, 

 are its surface features, the nature of the delthyrium 

 in the two valves, and the strong cardinal process and 

 median ridge in the dorsal shell. 



Discussion. — Otusia in general is a smaller and 

 differently shaped shell from Billingsella, being very 

 transverse and alate along the hinge-line. The sur- 

 face markings are more evenly spaced and rather more 

 uniform than is usual in Billingsella. A deltidium and 

 chilidium are lacking as far as present knowledge of 

 the genus goes. In the dorsal valve the brachiophores, 

 notothyrial platform, and cardinal process are precisely 

 as in Billingsella, perhaps a little more pronounced, but 

 this may be due to the progressive evolution and 

 younger age of Otusia. 



Even though Otusia is very close to Billingsella in all 

 its internal structures, the generic distinction appears to 

 be valid on the basis of its external form, sculpture, and 

 absence of deltidia or chilidia. 



Genus BOHEMIELLA Schuchert and Cooper 

 1931 



PI. l,figs. 1,3,5, 11, 18,22 



Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 

 1931, p. 242. 



Genoholotype. — Orthis romingeri Barrande 

 1848, Naturw. Abh. von Haidinger, vol. 2, pt. 1, 

 no. 5, p. 203, pi. 18, figs. 5a-d, as illustrated by 

 Walcott (1912, pi. 90, fig. 2). 



Description. Exterior. — Transversely suboval, 

 hinge-line straight, equal to the width of the valves, 

 cardinal extremities obtusely angular; lateral profile 

 piano- to concavo-convex; anterior commissure slightly 

 sulcate; dorsal sulcus broad and shallow. Ventral 

 interarea longer than dorsal, curved strongly, apsa- 

 cline; delthyrium open; dorsal interarea strongly 

 anacline, notothyrium open. Surface multicostellate; 

 test probably fibrous, impunctate. 



Ventral interior. — Delthyrial cavity deep, teeth 

 small, dental plates rudimentary ; muscular area faintly 

 impressed ; diductor scars on the sides of the delthyrial 

 cavity; adductor track wide and long; pallial marks 

 consisting of two sinuses extending directly anteriorly 

 to near the front margin where they bifurcate, the 

 outer branch continuing dorsally parallel to the anterior 

 and lateral margins; the inner branches converge 

 toward each other parallel to the anterior margin and 

 unite toward the middle of the shell. 



