42 KANSAS ACADEMY OF SCIENCE. 



the saddles at the umbilical shoulders are not so prominent. The young do not 

 seem to have the pilse so plainly shown in the umbilicus of Metac. cavatiformis, but 

 the cast may deceive the observer in this respect. 



Fig. 11 represents a section of the adolescent whorl without tubercles. 



DOMATOCEBAS, n. g. 



The species representing this genus is more closely allied to forms of Centroceras 

 than to those of any other genus, but these, so far as known, have very peculiar and 

 distinct characteristics. Although resembling this species in the external parts of 

 the transverse section of the whorls and in the sutures, they differ in many ways. 

 This is a true nautilan form, the impressed zone being a marked characteristic af- 

 fecting the dorsal outlines of the sutures in this species, whereas the typical centro- 

 ceran forms are gyroceran, having the impressed zone present only in the advanced 

 stages of growth of some forms. The nealogic stages in Centroceras remain simi- 

 lar to the adults of Temnocheilus for a prolonged period, and the tubercles remain 

 prominent, even on the casts throughout the later nealogic (adolescent) and earlier 

 ephebolic (adult) stages. No tubercles were observed in Domatoceras umbilicatmn, 

 although it was sufficiently well preserved to have shown them had they existed. 

 They might have been present in the earlier nealogic stages which were not visible. 

 In Centroceras, the young whorl throughout the later nealogic stages is tetragonal, 

 but the sides are divergent, the abdomen being broader than the dorsum. In this 

 species, during the same stages, the sides are nearly parallel or only slightly conver- 

 fient, and the abdomen nearly equal to or somewhat narrower than the dorsuta. 



Centroceras {Temnocheilus) Scottense (sp. Worthen, [see Geol. Surv. 111., VIII, pi. 

 27, fig. 3] ) is a good example of the genus Centroceras, having all the characteristic 

 markings and forms of that genus. 



DOMATOCEEAS UMBILIOATUM, U. S. 



Loc, Oswego, Kas. Lower coal measures. 



Coll. Nat. Mus., by Dr. Newlon. 



Fig. 12, natural size of living chamber at first septum. 



This species reaches a considerable size, the specimen here described being about 

 217 mm. in diameter. 



The living chamber is incomplete, and is a trifle over one-fourth of a volution in 

 length. The narrowing of the abdomen with increase of age is very marked on the 

 living chamber in this specimen. It measures 192 mm. in length along the abdo- 

 men, 73 mm. in the abdomino-dorsal diameter at the last septum, and about 52 mm. 

 in the transverse diameter at the umbilical shoulders, and 34 mm. near the venter. 

 The sides of the whorls are flattened and converge outwardly, so that the abdomen 

 is considerably less in breadth than the dorsum in the large, full-grown stage. There 

 is a shallow, impressed zone upon the dorsum, which occupies about one-third of its 

 width, and is due to the slight rotundity of the abdomen and the small amount of 

 involution in the coiling of the whorls. The umbilical shoulders stand out abrupt 

 and broad, giving a depth to the wide umbilicus, which is a marked characteristic. 

 The sutures have shallow, ventral lateral lobes. The saddles at the umbilical shoul- 

 ders are broad and extend inwards to the edges of the impressed zone, and then the 

 sutures bend toward the apex, forming a shallow dorsal lobe. There are no annu- 

 lar lobes in the center of the dorsal sutures. The siphon is above the center, and is 

 apparently nummuloidal. At the diameter of 95 mm., the whorl has the following 

 measurements: Abdomino-dorsal diameter, 41 mm.; transverse through the umbil- 

 ical shoulders, 32 mm., and breadth of the abdomen was 25 mm. 



Domatoceras (Nautilus) complanatum, sp. Sow. Min. Conch., pi. 2(51. from Isle of 



