120 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



Geologic range. — Ordovician to close of 

 Devonian. 



The family has the following genera: 



Dalmanella Hall and Clarke 

 Car'inijerella Schuchert and Cooper 

 Aulacella Schuchert and Cooper 

 Proschizofhoria Maillieux 

 Levenea Schuchert and Cooper 

 Heterorthina Bancroft 



Genus DALMANELLA Hall and Clarke 1892 



PI. 17, figs. 2-5, 7, 10, 13, 19-27, 29-31, 33; 

 t. fig. 8 



Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, pp. 205, 



223, pi. SB, figs. 27-39. 

 Sardeson, Amer. Geol., vol. 19, 1897, pp. 91-111. 

 €yn. Onniella Bancroft. 



Genolectotype (Schuchert and Cooper). — Or- 

 this testudinaria Hall and Clarke {non Dalman) 1892, 

 pi. 5B, figs. n-?,\=Orthl5 rogata Sardeson 1892, 

 Bull. Minnesota Acad. Nat. Sci., vol. 3, p. 331, pi. 5, 

 figs. 1-4. 



Description. Exterior. — Subcircular to subquad- 

 rate; hinge-line straight, narrower than the widest 

 part of the shell; cardinal extremities rounded ; lateral 

 profile piano- to very unequally biconvex; anterior 

 commissure sulcate, the sulcus usually being pro- 

 nounced; ventral fold faint or prominent. Ventral 

 palintrope longer than the dorsal, apsacline, beak in- 

 curved; delthyrium open. Dorsal interarea short, 

 anacline, notothyrium closed by the cardinal process. 

 Ornamentation fascicostellate, having prominent ele- 

 vated growth-lines in the interspaces. Test fibrous, 

 punctate. 



Ventral interior. — Delthyrial cavity deep, teeth 

 stout; crural fossettes deep; dental plates strong, 

 flaring somewhat anteriorly; muscle field bilobed in 

 front; diductor scars elongate, usually extending a 

 little anterior to the front end of the adductor track; 

 adjustor scars situated at the base of, or on the sides 

 of, the dental plates, usually narrow, elongate. Ad- 

 ductor track linear, narrow or wide. Pallial sinuses 

 consisting of a main trunk directed slightly antero- 

 laterally, taking its origin at the anterior ends of the 

 diductor impressions. It trifurcates shortly after its 

 origin, one trunk being directed antero-medially, one 

 antero-laterally, and a third secondary sinus extending 

 directly laterally. These secondary trunks break up 

 into subsidiary rami toward the margin. 



Dorsal interior. — Notothyrial cavity completely 

 filled by the cardinal process; brachiophores simple, 

 divergent, bladelike plates, subtrigonal in plan, sup- 

 ported only by adventitious shell deposited about the 

 cardinal process and on the inner side of the brachio- 

 phore. Cardinal process short, myophore trilobate or 



multilobate; median ridge low, extending nearly to 

 the front or terminating at the front margin of the 

 muscle field. The latter small, suboval or subcircular 

 in outline; anterior adductor scars the larger, separ- 

 ated from the posterior pair by low ridges at right 

 angles to the median elevation. 



Geologic range. — Middle Ordovician (Chazy) 

 to Silurian. 



American Species 



Orthis corfulenta Sardeson 1892 

 O. emacerata Hall 1860 

 O. futilis Sirdeson 1897 

 O. «^«o/a Sardeson 1897 

 O.meeki M\]\eT 1875 

 O. niultisecta Meek 1873 

 O. porrecta Sardeson 1897 

 O. rogata Sardeson 1892 

 Dalmanella bassleri Foerste 1909 

 D.resufinata Raymond 1921 

 D. whittakeri Raymond 1921 



? Orthis tersa Sardeson 1892 



European Species 



Dalmanella navis Opik 1930 

 Onniella avelinei Bincioh 1928 

 O. broggeri Bancroft 1928 

 O.reuschi Bancroft 1928 



Distinguishing characters. — ^The members of 

 this genus are to be recognized chiefly by the plano- 

 or nearly plano-convex profile, fascicostellate ex- 

 terior, bilobed ventral muscle area, and primitive 

 brachiophores. 



Discussion. — Hall and Clarke suggested the name 

 Dalmanella, first using it as the "Group of Orthis 

 testudinaria" under the genus Orthis. These authors 

 distinguished thirteen group names under the old genus 

 Orthis, but they never designated these "groups" as 

 genera or subgenera. In describing Dalmanella as the 

 "Group of Orthis testudinaria Dalman" they had be- 

 fore them American shells which they correlated with 

 Dalman's species. The group included, however, a het- 

 erogeneous lot from which several genera have already 

 been split. We will show that Orthis testudinaria 

 Dalman non Hall and Clarke actually belongs to a 

 group which is pretty much restricted to the Upper 

 Ordovician and early Silurian and is totally distinct 

 from the American Ordovician Dalmanellas with 

 which Hall and Clarke obviously dealt in their descrip- 

 tion of the group. This situation then brings up an 

 intricate nomenclatorial problem as to what the geno- 

 type of Dalmanella really is. If one adheres strictly 

 to the rules of nomenclature, he would say that Hall 

 and Clarke chose O. testudinaria of Dalman and the 

 European species should therefore constitute the type 

 of the genus. This would, however, restrict one of 

 our commonest names to an heretofore obscure divi- 



