186 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull.106. 



ences, therefore, between the two shells, and those which we deem of 

 specific importance, are the greater length of the deflected part, the 

 laterally compressed form of the volution, and the different direction of 

 the costre on the straight part of the shell. The two forms are associ- 

 ated at the same localities, and even occur in the same hand specimen 

 of rock, but we think there is no difficulty in distinguishing them." 



The septa of the two forms are essentially the same, the only differ- 

 ence being that those of the small specimens assigned to 8. ivyomingen- 

 sis are slightly less complex. In all of them the septa are much more 

 simple than in most species of the genus. The differences do not seem 

 to me great enough nor constant enough to warrant the reference of 

 these forms to distinct species, especially when we remember that they 

 are associated in the same stratum. Other species of Scaphites, such 

 as 8. nodosum, certainly show greater variations. For comparison, copies 

 are given of Meek's figure of the type of 8. tear rent and of Whitfield's 

 figures of 8. warreni and 8. wyominijensis. After careful comparison of 

 this species with Scaphites cequalis Sowerby, of the European Ceno- 

 manian, Prof. Meek regarded them as very closely allied. 



Locality and position. — The type came from the southern base of the 

 Black hills of Dakota, where it was found in the Fort Benton shales. 

 It has been collected from the some horizon at many localities in Wyo- 

 ming, Dakota, Colorado, New Mexico, and Utah. 



Scaphites ventricosus Meek & Hayden. 

 PI. xliv, Figs. 8-10 5 PI. xlv, Fig. 1. 



ScapMtes ventricosus Meek & Hayden, 1862, Proc. Acad. Nat. Sci. Pliila., p. 22; Meek, 

 1876, U. S. Gcol. Sur. Terr., vol. ix, p. 425, PL 6, Figs. 1 a,b ami 8 a, b. 



Eevised description: 



" Shell attaining a medium or larger size, oval, ventricose, broadly 

 rounded over the periphery; inner turns closely involute, deeply em- 

 bracing, and composing a large portion of the entire bulk- deflected 

 portion very short; umbilicus very small and deep; aperture trans- 

 versely sublimate or reniform, but deeply sinuous, and but slightly dis- 

 connected from the inner turns on the inner side] surface ornamented 

 with costae that pass nearly straight oyer the periphery, where they are 

 of uniform size, excepting their gradual enlargement with the volutions, 

 while on the sides of the last or outer volution, about every fifth or sixth 

 one is larger and more prominent than the intermediate ones, which 

 latter do not extend inward to the umbilical margin. 



" The septa, as made out from the specimen represented by our fig- 

 ures 8a, b (believed to be the inner volutions of this species, as repre- 

 resented by figures 7«, b) are provided with deeply divided lobes and 

 sinuses. Siphonal lobe longer than wide, and bearing on each side of 

 its very slender body three branches, the two terminals of which are 

 slightly larger than the succeeding lateral ones, and each unequally 



