114 AMERICAN JOURNAL 



Schloth., Dav. An. of Nat. Hist. 1850, pi. xv, figs. 5, a, b. The 

 structure of Stringocephalus, while sufficiently distinct to de- 

 serve a section to itself, is most nearly allied to that of the sep- 

 tate Waldheimias, near which I have placed it. 



Stringocephalus, according to Mr. Davidson, has only been 

 found in strata of the Devonian aa:e. 



Messrs. White and St. John have provisionally indicated a 

 new form under the name of Onjptacantlda, (Trans. Chicago 

 Acad. Sci., i. p. 119, 18(J8,) which presents some analogies with 

 Stringocephalus, Waldheimia and Terehratulina. "The loop 

 seems to be essentially like that of Waldheimia in form, but the 

 crura of the loop appear to be joined, * * * r^^^^ the loop- 

 band is armed with numerous spines which point outward toward 

 the shell (?) in all directions," W. and St. J. loc. cit. It can- 

 not be determined from this description whether the spines are 

 directed toward the margin or the body of one of the valves, but 

 it affords another argument against affiliating Stringocephalus 

 with MegatJiyris from the mere presence of such appendages. 



Type Waldheimia? compacta, W. and St. J. Tr. Chic. Acad. 

 Sci. I., p. 119, fig. 3, a, b, c. 



Section MAGASIN.E. 



Magasina, Gray, B. M. Cat., p. 85, 1853. 



Loop reflected, attached both to the hinge margin and to the 

 septum of the haemal valve. 



Genus TEREBRATELLA. 



Apophyses wuth their hasmal arms connected with the septum 

 by two (septal) processes. 



Subgenus Trigonosemus. 

 Trigonosemus, Ki>nig, Icon. Sect. 1825, p. 3, f. 73. [T. ele 



Fissurirostra, D'Orbigny, Pal. Fran. Cret. p. 133, fig. 520. 



(F. recurva), 1847. 

 Fissirostra, D'Orb., Cours. El. Pal., p. 89, 1849. 



Shell with produced curved beak or umbo in the neural valve ; 

 a tninute apical foramen ; a large triangular area, flat and 

 marked by the outline of the flat deltidium ; cardinal process 

 very prominent. Loop as in Terehratella. 



Type Trigonosemus elegans, Konig. Fossil in the Cret. 



I can only concur with ^Ir. Davidson in considering this sec 



