. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Orthoidea; Pentameroidea; Paleontology -- Paleozoic. GENERA OF THE SUBORDER ORTHOIDEA 95 European Species of Pl/Esiomys Orthis {Dinorthis) fabellulum carrickensis Rccd 1917 O. infijia Salter O. fore at a McCoy 1846 O. Solaris von Buch O. (D.) striato-costata Salter 186S O. \d.) suiJirisa Salter 1865 American Species of Retrorsirostra Dinorthis carUyi (Hall) 1860 D. carleyi insolens Focrste 1909 (Salter) 1858 Anticosti Species of Pionorthis Dinorthis carUtona Twenhofel 1928 Orthis sola Billings 1866 Distinguishing char
. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Orthoidea; Pentameroidea; Paleontology -- Paleozoic. GENERA OF THE SUBORDER ORTHOIDEA 95 European Species of Pl/Esiomys Orthis {Dinorthis) fabellulum carrickensis Rccd 1917 O. infijia Salter O. fore at a McCoy 1846 O. Solaris von Buch O. (D.) striato-costata Salter 186S O. \d.) suiJirisa Salter 1865 American Species of Retrorsirostra Dinorthis carUyi (Hall) 1860 D. carleyi insolens Focrste 1909 (Salter) 1858 Anticosti Species of Pionorthis Dinorthis carUtona Twenhofel 1928 Orthis sola Billings 1866 Distinguishing characters.—Dinorthis is char- acterized chiefly by its convexo-concave profile, svib- quadrate and anteriorly bilobate plan of the ventral muscle field, Or?/;w-type brachiophores, crenulated myophore, and pallial sinuses. From Orthis s. s. it differs in its contour, musculature, and pallial markings. Discussion.—Dinorthis of the Dinorthidae and Dolerorthis of the Orthidas form an interesting homoe- omorphic pair, but the two can be distinguished readily by their internal features. The ventral musculature of Dolerorthis is hke that of Orthis s. s. and never has the adjuster scars developed to any marked degree. The most important difference, however, is to be seen in the pallial and ovarian impressions of the two genera (see pi. 5, fig. 20, and compare with pi. 10, fig. 24). The pallial marks of Dolerorthis are of the Orthis type, two subparallel trunks given of? from the anterior ends of the diductor tracks and extending directly anteriorly. They are separated by a narrow septal ridge and bound ovarian impressions which occupy nearly the entire sur- face of the interior lateral spaces. In Dinorthis, on the other hand, the ventral pallial trunks are divergent and the ovarian impressions are greatly reduced. There is so much variation in the external contour and profile of Dinorthis that several distinct subgenera may be separated as follows: 1. D. fectinella—Dinorthis s. s. 2
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