GENERA OF THE SUBORDER ORTHOIDEA 



105 



Genus NOETLINGIA Hall and Clarke 1893 



Hall and Cl.irkc, Pal. N. Y., vol. 8, pt. 2, 1893, p. 229, 

 figs. 159-166. 



Genoholotype. — Spirifcr tscheffkim Dc Vcrneuil 

 1845, Geol. Russie, vol. 2, p. 129, pi. 2, figs. la-h. 



Distinguishing characters. — This genus differs 

 extern.illy from Porambonitcs chiefly in the wider 

 hinge-line and more distinctly developed interareas, 

 and internally in the presence of a simple linear car- 

 dinal process. 



Discussion. — Hall and Clarke figure a number of 

 "transverse serial sections" of a single specimen of 

 the genotype which illustrate the internal structure. 

 This is almost identical with that of Poramhotutes. In 

 the first section the dental plates are subparallel and 

 extend directly to the floor of the valve, and in all 

 the other cuts these plates continue discrete except 

 for the thickening at their bases. In the last two sec- 

 tions (figs. 165 and 166) the anterior ends of the 

 plates are coalesced at their bases and produced forward 

 as a median thickening. In the dorsal valve the brach- 

 iophore supports have a decided curve toward each 

 other, but the bases are always thickened and obscure. 

 It is unfortunate that the illustrations show no distinc- 

 tion between the primary growth of the plates and the 

 secondary adventitious shell. However, the sections 

 demonstrate that Noetlingia is on the whole very close 

 to Porambonites (see especially fig. 164), and as the 

 geological occurrence of the two is nearly identical, it 

 follows that Noetlingia is in all probability an offshoot 

 of Porambonites. 



Hall and Clarke (p. 229) remark that "the long, 

 double-areaed hinge-line, the biforate umbones and 

 suggestive external resemblance in contour to Platy- 

 strophia, forms a more strongly orthoid combination 

 than has been heretofore observed among shells with 

 such pronounced pentameroid affinities, and thus makes 

 a more direct connection between Porambonites and 

 the orthoid stock whence they have all been derived." 

 Under Porambotiites we have shown that these shells 

 belong in the Orthacea, and this conclusion is further 

 supported by the evidence of Noetlingia with its orthoid 

 cardinal process and wide interareas. 



Family LYCOPHORIID^ Schuchert and 

 Cooper 1931 



Aberrant Orthacea derived out of the Orthidae, 

 biconvex, having strong dental plates and in the dorsal 

 valve a simple cardinal process intimately united with 

 the brachiophore plates. 



Geologic range. — Lower Middle Ordovician of 

 the Baltic provinces. The only genus is Lycofhoria 

 Lahusen. 



Genus LYCOPHORIA Lahusen 1886 



PI. 14, figs. 16-19, 22, 23, 25, 26, 30 



L.-ihuscn, Verh. Russ. Min. Gescll., ser. 2, vol. 22, 1886, 



p. 221. 

 Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 230, 



pi. 62, figs. 49-53. 



Genoholotype. — A try fa nucella Dalman 1828, 

 K. Vet. Ak.nd. Handl. for 1827, p. 130, pi. 5, fig. 1. 



Description. Exterior. — Outline globular or 

 elongate-ovoid, hinge-line straight, narrower than the 

 total width of the shell, cardinal extremities obtusely 

 angular. Lateral profile strongly biconvex, the dorsal 

 valve having the greater convexity. Anterior commis- 

 sure straight or moderately uniplicate. Dorsal fold 

 visible at the front of the valve only. Ventral inter- 

 area very short, apsacline, delthyrium open ; dorsal 

 interarea obsolete. Beaks very small. Surface costel- 

 late ; test fibrous, impunctate. 



Ventral interior. — Delthyrial cavity deep; teeth 

 large, with deep sockets; parallel to the hinge-line; 

 extremity of tooth with a dorsad curvature ; dental 

 plates strong, extended forward as subparallel ridges 

 nearly to the middle of the valve. In old shells the 

 umbonal cavities are filled with adventitious deposit. 

 The muscle field is bounded by the dental plates. The 

 adductor scar is small, subcircular, and enclosed in 

 front by the diductors, which are elongate and con- 

 vergent in front. A low ridge separates their anterior 

 ends in some species and is continued forward toward 

 the front of the shell. Attachment of pedicle marked 

 by a callus in the delthyrial cavity. 



Dorsal interior. — Notothyn'al cavity obsolete, brach- 

 iophore plates and cardinal process fused, forming a 

 trituberculate "tooth" or process which projects into 

 the ventral valve. "Crura" are small nubs on each 

 side of the cardinal process. On the dorsal surface 

 of the cardinal process is a small chilidial plate similar 

 to that seen in Productorthis. Muscle area quadri- 

 partite, posterior pair subtriangular or subtrapezoidal 

 with thickened elevated lateral margin. Anterior 

 scars forming a quarter of an ellipse in plan, divisible 

 into two parts, an inner larger scar and a smaller 

 outer scar. 



Geologic range. — Lower Middle Ordovician 

 (Kunda formation, B3) of Europe. 



Species 



A try fa nucella Dalman 

 Rhynchonella globosa Eichwald 

 R. jrenum Eichwald 



Distinguishing characters. — The globular form 

 and strong biconvexity of Lycofhoria, together with 



