ART. 17 MOLLUSKS FROM WYOMING — REESIDB AND WEYMOUTH 15 



Four of the genera may be instantly excluded from consideration 

 here, but Metengonoceras and EpengOTWceras must be taken into 

 account. The original description of Metengonoceras brought forth 

 as its chief characteristic the sharpening of the venter in the middle 

 stages of growth, preceded by a stage with truncated venter and 

 succeeded by a final stage with rounded venter. Epengonoceras was 

 separated by Spath for Cenomanian and Turonian species from 

 Metengonoceras apparently in the main because of its younger age, 

 for citation of Hyatt's figure and description of the Turonian species 

 ^''Metengonoceras''' dunibli (Cragin) Hyatt was the only character- 

 ization given. These fit in every respect the characterization of the 

 typical Albian Metengonoceras. However, Hyatt's description of 

 dumbli is in error in the important respect that the venter is not 

 at any stage acute but retains a narrow truncation to a late stage and 

 then becomes rounded. An examination of the specimen figured by 

 Hyatt and cited by Spath is sufficient to convince that it is only the 

 inner mold of the shell that is narrowly rounded, whereas the ex- 

 terior of the shell itself was channeled or flat on the periphery. 

 Hyatt interpreted a truncation of the latest part of the type pre- 

 served as due to injury to the shell, but it appears to the writers as a 

 normal feature. The writers have in hand about a dozen other speci- 

 mens from the Eagle Ford shale of Texas, which yielded the type. 

 and these show the feature even better than Hyatt's specimen, for 

 much more of the shell is retained, and some specimens even in the 

 internal mold show a distinct ventral facet. The generic description 

 given above is drawn up in accordance with these observations. 



The writers have in hand also four specimens figured by Hyatt as 

 Metengonoceras inscripfu7n^ including the type of the species and 

 genus, and one, the type, of M. amhiguum. All are more or less 

 corroded and deformed, and there is no trace of the shell on any of 

 them. It is not possible to say from these specimens v/hether the 

 sharp venter of the middle stages is an accident of preservation or 

 an original feature, nor whether the shell was flattened on the venter 

 or sharp. The suggestion is very strong, however, that the shell of 

 these Albian forms also had a narrow, flattened, or concave venter, 

 even though the molds may have been more or less acute. In fact, 

 the front view ^^ of the type of M. wsoiptum given by Hyatt is much 

 restored and the specimen does not show any such straight, sliarp 

 ventral edge as his figure presents. On the contrary the venter is 

 irregular, and one part lying between sharpened parts shows a dis- 

 tinct truncation, suggesting that the sharp parts are deformed and 

 the flattened part normal. The writers feel that questions as to 

 Metengonoceras must remain unsettled until some one is fortunate 



'^ Hyatt, Alpheus, U. S. Geol. Survey Mon. 44, pi. 25, fig. 9. 



