48 



Report of the State Geologist. 



would be the natural outcome of a continuation of development beyond the 

 extreme attained by Mantic. Patterson!. Styliophihim is, thus, in the form of its 

 whorls, a progressed type. Its sutures, however, are less extreme in the develop- 

 ment of lobes and saddles than in Pattersoni. In respect to the degree of 

 umbilication there is no appreciable departure from the normal. 



This form is undeniably interesting as characterizing the earliest manifes- 

 tation, in the New York faunas, of the entire Intumescens group. The same 

 form very seldom appears in the second manifestation of the fauna. Accom- 

 panying the var. styliophihwi in the prenuncial fauna are two forms to which 

 attention may here be briefly directed: the species Mantic. contrccctu m and Ma n f i< - 

 apprimatv/m. Both have the aspect in gross of Mantic. Pattersoni, but are both 

 much more closely umbilicated shells, of persistently smaller habit. Monti- 

 coceras contractual has a very distinct ornamentation, showing upon the late 

 whorls a fasciculation of the striae into ridges and a convexity of whorls which 

 together (and we have not much else to rely upon thus far in construing the 

 species) separate it pretty widely from the Intumescens type. The other, 

 Mantic. apprimatum, has a broadly sloping final whorl and, in respect to orna- 

 mentation, shows that the elementary period during which the simple, con- 

 tinuous varices were introduced, was of much longer duration than in Mantic 

 Pattersoni, and we find these lamellae without intercalations extending forward 

 through the third volution ; farther indeed than in the species Mantic. 

 tardum, where a similar character obtains, accompanied by much greater 

 umbilication than in either Mantic. Pattersoni or Mantic. apprimatum. 



Development of Form. Such observations as are here made in regard to 

 the modification of the shell-form with growth are largely based upon delicate 

 barite replacements of young shells which preserve in marvellous perfection the 

 details of structure and ornament. These specimens, which in many cases repre- 

 sent the entire shell in various stages of early growth, have been derived almost 

 w holly from isolated calcareous concretions in the lower part of the Naples beds 

 about Honeoye lake, in the towns of Richmond and Canadice, Ontario county 

 a few have been obtained from similar concretions taken farther westward, in 

 Livingston county, about Conesus lake. In the Canandaigua lake valley or 

 westward in Yates county, none have been found in this mode of preservation, 

 and evidences of these young shells are comparatively rare in the shales. 



The apparent regional abundance of these young, may be due to their 

 being rendered conspicuous objects by the white or pinkish barite which has 

 replaced the original shell substance, but that they do thus abound and that 

 the observations here put forth are not insufficiently grounded is evinced by 



