()8 COLORADO COLLEGE STUDIES. 



Two species of Ndidilus are common iti the rocks of the 

 Washita division, viz., X. fcxduus, Shumard, and N. washi- 

 taims, nobis, which have hitherto been confounded, owing to 

 their ,o:eneral external resemblance and the fact that, occur- 

 rin<2: more commonly as fragments than as complete speci- 

 mens, they often cannot be easily distinguished except by the 

 position of the siphuncle, which is frequently not shown. 



All of the critically available specimens of Nautilus that 

 the writer had observed from rocks of the Washita division, be- 

 fore the publication of his " Contribution to the Invertebrate 

 Paleontology of the Texas Cretaceous," had the siphuncle in 

 the dorsal (outer) half of the septum, and the writer there- 

 fore stated in that report that Shumard was in error in 

 alleging its position to be ventral. The writer is now ac- 

 quainted with two types of Nautilus from the Washita 

 division and now admits the accuracy of Bhumard's descrip- 

 tion. So far as observed, however, the common species of the 

 Washita limestone is N. loashitanus, the Nautilus of the 

 Denison beds being ordinarily N. texanus, as shown by its 

 having the siphuncle nearly at the limit between the ventral 

 (inner) and the middle third of the septum. The latter 

 species has been found by the w^-iter in the Denison beds of 

 Denton and Grayson counties, Texas, and ranges up into the 

 highest terrane of these beds, viz., the Grayson marl. 



