. Bulletin - New York State Museum. Science. 460 NEW YORK STATE MUSEUM chamber and the preceding chamber. The specimen was obtained at Pickett's Station [now called Dill], Wise. It is, in its rate of growth, absolutely identical with E. kelloggi, nor does it ap- pear to differ sufficiently in section, position of siphuncle and depth of septa to warrant specific differentiation. Eurystomites accelerans sp. nov. Plate 18, fig. 2, 3 We have a specimen from A3 of the Fort Cassin beds at Val- cour, which in the rate of growth of the conch, the section of the whorls and position of the siphuncle ful
. Bulletin - New York State Museum. Science. 460 NEW YORK STATE MUSEUM chamber and the preceding chamber. The specimen was obtained at Pickett's Station [now called Dill], Wise. It is, in its rate of growth, absolutely identical with E. kelloggi, nor does it ap- pear to differ sufficiently in section, position of siphuncle and depth of septa to warrant specific differentiation. Eurystomites accelerans sp. nov. Plate 18, fig. 2, 3 We have a specimen from A3 of the Fort Cassin beds at Val- cour, which in the rate of growth of the conch, the section of the whorls and position of the siphuncle fully agrees-—at least at a certain stage, represented by the last whorl of our fragment — with E . kelloggi; but differs from that species by the very marked fiat ventral zone, the closer position of the septa (5 in 20 mm where the hight of the volution is 23 mm, against 4 under the same con- dition in E . kelloggi) and their stronger forward curvature near the line of involution. In the fiat ventral zone, the closer ar- rangement of the septa and the dorsal direction of the sutures, this form suggests the genus Tarphyceras as represented by Tarphy- c e r a s c h a m p 1 a i n e n s e , but the rate of growth of the whorl prohibits a reference to that species or to the genus Tarphyceras. There is little doubt that this is a new form which represents a more advanced stage in the phylogenetic development of the Eurystomites race than E. kelloggi. This is shown specially in the early ap- pearance of the ventral zone and the greater amount of curvature of the suture whicli here in the neanic stage is already much greater than that in the ephebic stage of E. kelloggi. A certain amount of acceleration in the development of the characters as compared with the latter species has therefore taken place. E. Virginian us also has more numerous sutures than E . kelloggi, but these are described as straighter than those of E . kelloggi in all stages. In this particular character it is henc
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