2 72 NEW YORK STATE MUSEUM 



(certainly an extreme development of the series of forms) has a broad sub- 

 cardinal area, which Freeh compares with the ligamental surface in 

 Limoptera. There is further an aviculoid aspect apparent in the smaller 

 valve, and also, by bringing into comparison with this bizarre shell certain 

 Triassic genera of similar aspect, Hoernesia and Cassianella, the modified 

 Avicula form is emphasized. It loses itself in Loxopteria by the disap- 

 pearance of all trace of ligament area and wing (except on the right valve), 

 and yet a certain resemblance to Kochia in form and the relations of 

 the valves is evident. The extreme in this suppression of characters is 

 attained in the forms we have referred subgenerically to Sluzka, and yet 

 their immediate affiliation with typical expressions of Loxopteria is clear. 



Loxopteria dispar Sandberger (sp.) 



Plate 13, fig. 8-17 



Avicula dispar Sandberger, Versteinerungen des rhein. Schichtensyst. in 



Nassau, p. 284, pi. 29, fig. 14 

 Avicula dispar Kayser, Studien aus dem Geb. d. rhein. Devon, 4; Zeitschr. der 



deutsch. geol. Gesellsch. 1893. p. 636 

 Kochia (Loxopteria) dispar Freeh, Devon. Aviculiden Deutschlands ; 



Abhandl. z. geolog. Specialkarte Preuss. u. d. Thiir. St. 1891. v. 9, Heft 3, 



p. 77, pi. 6, fig. 4 - 4 h. 



Shell subtriangular in general outline. Valves highly unequal in form 

 and contour. Left valve subtrihedral, umbo convex, beak incurved and 

 anterior. Posterior outline abruptly sloping to the ventral margin. 

 Anterior margin incurved beneath the beak, expanding somewhat to the 

 broad anteroventral curvature. Ventral margin transverse or curving with 

 a broad inward undulation to the posterior ridge. Slope of the surface 

 from the posterior or umbonal ridge sharply incurved to the periphery with 

 no trace of wing. Anterior slope broad and faintly depressed beyond the 

 body of the shell. Surface with a few broad radial ribs or undulations of 

 variable number and size. These are all usually sharply defined at the 

 umbo, are three or four in number and broaden out over the body, becoming 

 obscure or obsolete about the margin. There is much variation in the 



