GENERA OF THE SUBORDER ORTHOIDEA 



75 



by homologizing the muscle impressions and pallial 

 sinuses of the ventral valve and the cardinalia. Rem- 

 nants of dcltidia within the Orthido; are further links 

 of relationship with the Billingsellid.T. The cardinalia 

 of BUimgsella and Eoorthis are enough like those of the 

 Orthida: to hold that the one could have been derived 

 out of the other. We believe it probable that the 

 Hespcrorthinx and Glyptorthina; were derived from 

 Eoorthis of the Eoorthid.x, but the Orthina; of Europe 

 appear to us to have been derived out of Billingsella 

 or some unknown ancestor closely related to that 

 genus. The origin of the Orthida: can not be stated 

 with any degree of precision because the Cambrian and 

 Ozarkian articulate brachiopods and Cambrian and 

 Ozarkian stratigraphy of the world are too little known 

 at present to warrant more than suggestions. 



We propose to subdivide the family Orthids into 

 the following subfamilies, all of Schuchert and Cooper 

 1931: 



Orthinae TaflSins 



Productorthinae Hesperorthins 



Angusticardiniina: Glyptorthina 



The lines 6f genetic descent seem to be about as 

 shown in Table 5. 



Subfamily ORTHINA Schuchert and Cooper 1931 

 (Not Orthinae Waagen 1884 = mainly Orthidae) 



Progressive Orthidse having short and strongly 

 curved ventral interareas, with strongly incurved ven- 

 tral beak. So far as known, a deltidium or any rem- 

 nant of such a structure has never been seen in the 

 Orthinae as here defined. Chilidial plates are also rare 

 in occurrence. 



Geologic range. — Lower and Middle Ordovician. 



The members of the Orthin.-E are chiefly European 

 in origin and differ quite markedly in the contour 

 and profile of the shell from the representative Ameri- 

 can stock typified by Hesferorthis. The European 

 genera invariably have short curved interareas and are 

 never provided with a deltidium or complete chilidium. 



The subfamily contains the following genera: 



Orthis Dalman 



Cyrtonoiella Schuchert and Cooper 



Nicolella Reed 



Glossorthis Opik 



Paurorthis Schuchert and Cooper 



? Archteorthis Schuchert and Cooper 



Genus ORTHIS Dalman 1828 (sensu stricto) 



PI. 2, figs. 7-13, 15-18; t. figs. 3, 11 



Dalman, K. Vet. Akad. Hand], for 1827, 1828, pp. 93, 96, 



pi. 2, fig. 3. 

 Davidson, Brit. Foss. Brach., vol. I, Introd., 1853, p. 101, 



pl. 7, fig. 127. 

 Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, pp. 191- 

 194. 



Genolectotvpe (Davidson). — Orthis callactis 

 Dalman as above cited. 



Description. Exterior. — Subsemicircular to semi- 

 oval, anterior margin convex; lateral margins con- 

 vex to concave; hinge-line wide and straight, rarely 

 subalate; lateral profile plano-convex to unequally 

 biconvex, occasionally concavo-convex; lateral com- 

 missure usually straight; anterior commissure recti- 

 marginate, dorsal valve provided with a faint median 

 sulcus. Ventral interarea short but longer than the 

 dorsal one, curved; ventral umbo swollen, beak 

 strongly curved, interarea faintly apsacline or nearly 

 orthocline; delthyrium open. Dorsal interarea plane, 

 strongly anacline, notothyrium open. Ornamentation 

 paucicostate, costae and interspaces covered by parvi- 

 costellae and faint lines of growth. Test fibrous, 

 impunctate. 



Ventral interior. — Delthyrial cavity deep, teeth 

 strong, crural fossettes very deep; dental plates strong, 

 obsolete in old shells; muscle area confined to the 

 delthyrial cavity, oval in outline; adductor scars cen- 

 trally situated, forming an elongate track; diductor 

 impressions extending as far forward as the end of 

 the adductor track, and partially placed on the sides 

 of the dental plates; adjustor scars not distinguish- 

 able; pedicle callist rarely visible in the apex. Pallial 

 markings consisting of two trunks, one given off from 

 the front end of each diductor scar and extending 

 beyond the middle of the shell, where they are abruptly 

 curved away from each other. Anterior margin crenu- 

 lated by coarse ribs corresponding to the strias of the ex- 

 terior, each rib bearing an elevated ridge on its margin. 

 Dorsal interior. — Notothyrial cavity shallow; car- 

 dinalia confined; sockets deep, excavated slightly be- 

 neath the palintrope; brachiophores forming the 

 margin of the notothyrial cavity, short and simple, 

 unsupported except for the deposition of shell material 

 around them in the building up of the notothyrial plat- 

 form; cardinal process a simple ridge of variable 

 thickness, probably bearing two muscle attachments; 

 in some species diductor scars are visible on the noto- 

 thyrial platform on each side and at the base of the 

 cardinal process. Notothyrial platform a thickening of 

 the valve forming the floor of the notothyrium, ex- 

 tended forward to the anterior margin of the adductor 

 scars as a median ridge. Muscle area small, not oc- 

 cupying more than one-third the length of the valve; 

 adductors small, the anterior pair the larger. Pallial 

 markings four, one pair given off from the antero- 

 lateral margin of the anterior adductors, the other 

 from the anterior end of the median ridge. 



Geologic range. — Lower and Middle Ordovician. 



American Species 



O. butlsi, new name" 

 O.fanderiana Hall and Clarke 1892 



'^ For O. crasicosta Butts (non Pander), Gcol. Surv. 

 Alabama, Spec. Rept. 14, 1926, p. 116, pl. 26, figs. 14-15. 



