ALLORHYNCHUS 197 



from the genus Pugnax and bring it in conformity with the members 

 of the genus Pugnoides which possess the median septum in the brachial 

 vave and the crural cavty between the opposite parts of the divided hinge- 

 plate. The species is one of the rarest forms in the lower Burlington lime- 

 stone. 

 Horizon. Fern Glen formation, lower Burlington limestone. 



Genus ALLORHYNCHTJS Weller 



Description. Shells rhynchonelliform, small or below medium size, with 

 mesial fold and sinus well developed and both valves marked by sub- 

 angular or rounded plications which are usually well denned to the beak. 

 Interior of the pedicle valve with slender dental lamella?. In the brachial 

 valve the hinge-plate is divided, the inner edges of each lateral portion 

 being unsupported, no median septum and no crural cavity, such as is 

 present in Camarotcechia are developed. 



Remarks. In external features the members of this genus are not essen- 

 tially different from Camarotcechia, but an examination of the interior 

 of the rostral portion of the brachial valve shows that they are not at all 

 alike. In the entire absence of lamellae of any sort for the support of the 

 hinge-plate of the brachial valve, Allorhynchus is like Pugnax, but it 

 differs from that genus in the completely plicated shell. 



ALLORHYNCHUS HETEROPSIS (Winchell) 

 Plate XXIV, Figs. 73-81 



1865. Rhynchonella heteropsis Win., Proc. Acad. Nat. Sci. Phil., p. 121. 

 1901. Camarotoechia (?) heteropsis Weller, Trans. St. Louis Acad. Sci., 



vol. 11, p. 156, pi. 13, figs. 9-13. 

 1910. Allorhynchus heteropsis Weller, Bull. Geol. Soc. Am., vol. 21, p. 



509, fig. 8. 



Description. Shell small, triangularly subovate in outline, usually wider 

 than long, the greatest width anterior to the mid-length of the shell, the 

 postero-lateral margins nearly straight or a little sigmoidal and meeting 

 at the beak in an angle from 90 to 108 degrees, the antero-lateral margins 

 rounded and the anterior margin straight or convex. The dimensions of 

 two individuals are: length 11.1 mm. and 12 mm., width 13.6 mm. and 

 12 mm., thickness 7.5 mm. and 6.4 mm., width of sinus in front 9.3 mm. 

 and 7 mm. 



Pedicle valve convex on the umbo, the surface curving rather abruptly 

 to the cardinal margin with the edges of the valve narrowly inflected for 

 a short distance on each side of the beak, towards the antero-lateral 

 margins the surface is gently convex or flattened and from the beak to 

 the front margin it is rather strongly arched; the sinus originates near 



