Geol— Vol. I.] SMITH— LYTOCERAS AND PHYLLOCERAS. 137 



almost smooth, but has fine sinuous cross-strise of growth that bend forward 

 on the abdomen, form a broad backward bend or lobe on the abdominal 

 shoulders, and another forward sinus on the sides. These are exactly par- 

 allel to the mouth, which is marked by varices and constrictions. The 

 growth lines scarcely show on internal casts, but the constrictions are quite 

 distinct, showing them to have been formed by thickening the lip of the 

 aperture during periodic cessations of growth. The sculpture of the shell 

 is shown on PI. XVII, fig. 4, diameter 7.50 mm., three and three-quarters 

 whorls, seven times enlarged. The shell is not smooth during all the stages ; 

 up to the end of the first coil it is smooth, then comes a deep constriction, 

 and for an entire coil the shell is ornamented with relatively coarse, single 

 cross-ribs, which end abruptly, and are represented in later growth by occa- 

 sional irregular varices. The spiral of the adult is shown on PI. XVII, fig. 6, 

 and a cross-section, early adult stage, on fig. i. 



The septa are like those usually found on Lytoceras, a long, divided 

 siphonal lobe, two principal lateral lobes divided into two parts, and an aux- 

 iliary lobe on the umbilical border, divided into several small secondary 

 lobes. This is really a part of the internal lateral lobe. All the lateral sad- 

 dles are deeply divided. PI. XVIII, fig. 14, shows the outside septa of the 

 largest specimen where they were visible, diameter 7.00 mm. 



It is quite likely that the adult grows considerably larger 

 than any specimen obtained, and that the septa grow more 

 complicated than this, but they would undoubtedly be very 

 like these, for they already bear the stamp of maturity. 

 The internal septa at this size could not be made out in 

 detail. 



The largest specimen obtained was only 14.5 mm. in 

 diameter, but from about six millimetres up there is little 

 change, so that larger sizes, if found, will probably be like 

 those figured and described in this paper. The cross- 

 section (PI. XVII, fig. i) shows that successive whorls 

 become only very gradually higher, and the abdominal 

 shoulders less rounded, so that there is small likelihood of 

 failure to recognize larger specimens of this species. The 

 only other species with which Lytoceras alaniedense might 

 be confused is an undescribed form collected by Mr. F. M. 

 Anderson at the Forty Nine mine, near Phoenix, Oregon, 

 and that has a lower, broader whorl, and deeper umbilicus 

 at the same size. The young stages of L. hatesi Trask are 

 slenderer, with rounded aperture like the adult, but with 

 simple adolescent lobes at diameter of 10 mm., and even at 

 that stage almost no impressed zone. They have many 



