Hyatt.] 296 [April 4, 



is striated longitudinally with fine closely set ridges even in full- 

 grown shells. The siphcn is nummuloidal, and above the centre. 

 The whorls vary in section from rounded to elliptical, and even 

 depressed elliptical outlines. The living chamber in Apl. (Cyrt.) 

 rostratum, sp. DeKoninck, ibid, pi. 35, is contracted slightly at 

 the aperture. The type is Apl. Verneuillianum. sp. DeKon., Calc. 

 Carb., pi. 34. The nearest armies of this genus seem to be in the 

 genus Sactoceras. 



Aipoceras, 1 nobis, includes the Carboniferous gyroceran forms 

 of which we know but one species, Aip. (Gyr.) gibberosum, de- 

 scribed by DeKoninck, Calc. Carb. pi. 32. This has a similar 

 whorl and is evidently a close affine of Aploceras, but the siphon 

 is tubular, and close to the venter as in Asymptoceras. The 

 smoothness of the shell, also, is transitional to this last named 

 genus, as well as the more compressed outline of the whorl in 

 section. The sutures retain the simple outlines of the arcuate 

 radicals, having slight ventral and dorsal saddles, or nearly 

 straight outlines. Mus. Comp. Zool. 



Asymptoceras, Ryckholt, Not. sur Asymp. et Vest. 1852, has 

 for its type, according to DeKon., Calc. Carb. p. 112, Phillips' spe- 

 cies of Naut. cyclostomus. Solenocheilus, Meek, is a synonym, 

 having for its type Asympt. (Naut.) Springeri W. & St. J., Tran. 

 Chic. Acad. Vol. 1, p. 124. The whorls increase very rapidly in 

 size, the living chambers are short with flaring, or slightly con- 

 tracted apertures. The venter is flattened, or slightly hollow 

 along the centre. The sides are more or less gibbous, and the 

 umbilical shoulders project in heavy ridges, or a large pair of 

 tubercles. Upon each side of these are flutes which are specially 

 characteristic. The dorsum is also remarkable for having the 

 centre gibbous as in gyroceran forms, indicating the recent der- 

 ivation of the genus from more loosely coiled forms. The sutures 

 have broad ventral lobes, saddles at the abdominal ridges, broad 

 lateral lobes, saddles at the umbilical shoulders and dorsal lobes, 

 with small annular lobes. Siphon is near the venter. 



The elliptical form of the young whorl, the large umbilical per- 

 foration, the simple, fine, smooth, longitudinal ridges, evenly dis- 

 tributed around the whorl, indicate derivation from Aipoceras. 



Aliriisi lofty or high. 



