. Bulletin - New York State Museum. Science. BEEKMANTOWN AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 5O3 must be assigned to a genus with more primitive characters than Gomphoceras has; and is evidently a member of Hyatt's genus Cyclostomiceras. The hyponomic sinus is shallow and narrow, and situated opposite to the marginal, tubular, nar- row siphuncle. The slight contraction of the living chamber is largely due to a thickening of the shell in apertura! direction [see text fag. 57], evidently a gerontic feature. On casts of the living chamber one observes as in C. cassinense a deep con- ^'ft&quo
. Bulletin - New York State Museum. Science. BEEKMANTOWN AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 5O3 must be assigned to a genus with more primitive characters than Gomphoceras has; and is evidently a member of Hyatt's genus Cyclostomiceras. The hyponomic sinus is shallow and narrow, and situated opposite to the marginal, tubular, nar- row siphuncle. The slight contraction of the living chamber is largely due to a thickening of the shell in apertura! direction [see text fag. 57], evidently a gerontic feature. On casts of the living chamber one observes as in C. cassinense a deep con- ^'ft"m^c'e^ras striction just posteriorly of the aperture, which is whit/'""(sp) produced by a ringhke thickening of the apertural t^d'inaf section margin. /\lso two parallel vertical carinae of un- ln^[^"'of "^shiii equal strength may be seen passing along the si- ?ure"'^x ^^^^' phuncular side of the cast. The species has not yet been observed outside of the beds at Fort Cassin. Genus oncoceras Hall emend. Hyatt Oncoceras pristinum sp. nov. Plate 34, figure i, 2 Description. Small, very breviconic cyrtoceracone. which is but slightly curved, the arc described by the outer margin having a hight of 7 mm, when the length of the conch is 30 mm; compressed, the dorsal side rounder than the ventral; the greatest diameter — which is the dorsoventral one, at about the first half of the living chamber — is 18 mm, the transverse diameter at the same place is about 14 mm. The living chamber slightly and gradually con- tracting in the last half; not quite occupying one half of the conch. Aperture apparently not contracted. Cameras shallow, 9 within the space of 10 mm in the ephebic part of the conch; the septa but little concave, their depth being about equal to that of one chamber, rising toward the outer side of the conch. Siphuncle very slightly nummuloidal, i mm wide, marginal at the outer side of the conch, without deposits. Surface smooth. Position and loca
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectscience, bookyear1887
