342 GEOLOGICAL SURVEY OF TEXAS. 



appeared before the inner lateral row during the Temnocheilus-like stage. 

 The side view (Fig. 44) has the lower part or outer whorl much too broad, 

 and the umbilicus consequently too narrow, but the depth is better shown 

 than in the other figure (Fig. 43), where it is a restoration. The notable fact 

 is the late stage at which the Temnocheilus form still characterizes the whorl 

 and the rapidity with which the sides become flattened and assume the Taino- 

 ceran outline. 



This species differs from Tainoceras quadrangulum, McChesney, in having a 

 stouter whorl in all its diameters and in the sutures, especially on the abdo- 

 men (outer side). The abdominal lobe is as broad as the outer side in quad- 

 rangulum, whereas in this species it occupies only the longitudinal concave 

 zone between the two rows of abdominal tubercles. It is more closely allied 

 to Nautilus tuberculatus, Sow., as figured by Trautschold,* from the Upper 

 Carboniferous of Russia, but the shell has whorls broader in proportion to 

 the abdomino-dorsal diameter, and the nodes of the outer lateral ridges are 

 closer together and larger. Nautilus tuberculatus as figured by Sowerby ap- 

 parently differs in the same characteristics, but the figure is poorly executed, 

 and I have no English specimens of this species for comparison. 



This species might be supposed to be a close ally of Solenoceros [Nautilus) 

 Canaliculars as figured in the Kentucky Geological Survey, \ but the sutures 

 and all characteristics differ essentially in the adult stage, although the young 

 are quite similar. The Nautilus decoratus of the Kentucky SurveyJ may also 

 be the young* of an allied species of this genus, but is evidently not very 

 closely allied, since the abdominal depression is not very well marked in the 

 drawing. 



DOMATOCERAS, N. G-. 



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

 troceras 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 Nautilian form, the impressed zone 

 being a marked characteristic affecting the dorsal outlines of the sutures in 

 this species, whereas the typical Centroceran forms are gyroceran, having the 

 impressed zone present only in the advanced stages of growth of some 

 forms. The nealogic stages in Centroceras remain similar 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 ephe- 



*Kalkbruche von Miatschkowo, p. 28, PI. 3. 



fMaps and Illus. of Yols. II and III, 1857, PL x, Fig. 3 and Fig. 3a. 



JIbid, PI. ix, Fig. 4. 



