DIELASMOIDES 253 



inflected towards the cardinal extremities, gently convex to the antero- 

 lateral and anterior margins ; mesial sinus obsolete ; the beak a little flat- 

 tened, incurved, pierced by a rather large foramen which encroaches upon 

 the umbonal region. Internally the dental lamellae are well developed and 

 of moderate length. 



Brachial valve subequally convex with the pedicle, its greatest con- 

 vexity near or posterior to the middle, the surface curving more abruptly 

 to the postero-lateral margins and gently to the antero-lateral and an- 

 terior margins; neither mesial fold nor sinus present; the beak pointed, 

 incurved beneath that of the opposite valve. Internal characters not 

 determined. 



Remarks. In the preparation of the original description of this species 

 Winchell probably had two or more different forms in hand. The type 

 specimens are said to have come from the upper "Yellow sandstone" and 

 the "Oolite bed" of the Kinderhook at Burlington, Iowa, and it is said 

 also to occur at Hamburg, Illinois, and Talmadge, Ohio. In the original 

 definition a specimen from the upper yellow sandstone was used as the 

 basis for the description of the pedicle valve, and specimens from the 

 oolite were used for the description of the brachial valve and the shell 

 structure. It is probable that these specimens belong to two different 

 forms, and the form from the yellow sandstone will here be considered 

 as the type of the species. The true generic characters of this yellow sand- 

 stone species has not been determined, and cannot be in the condition 

 of preservation in which specimens have been found. It can be clearly 

 seen, however, that they do not possess a median septum in the brachial 

 valve and therefore cannot belong to the genus Girtyella, neither do they 

 have the crural lamelke resting upon the inner surface of the valve as in 

 Dielasma, and the species can therefore be excluded from that genus. The 

 specimens from the Hamburg, Illinois, locality are certainly examples of 

 the shell which has here been defined as Hamburgia typa, and while the 

 yellow sandstone specimens are certainly specifically different from these 

 Hamburg shells, it is still possible that they belong to the same genus. 

 The species is referred to Cranwna, however, because on the whole its mem- 

 bers seem more closely to resemble other species of that genus than 

 anything else. 



Horizon. Kinderhook. 



Genus DIELASMOIDES Weller 



Description. Shell terebratuliform. Pedicle valve bisinuate towards 

 the front in the genotype, the two depressions separated by a low, broadly 

 rounded mesial elevation; the dental lamellae well developed internally; 

 the foramen large, oblique, encroaching wholly upon the umbonal region. 

 Brachial valve with a slight mesial flattening or depression anteriorly 



