98 University of Texas Bulletin 



saddle although about as broad or even broader. It was impossible 

 to observe the suture on the umbilical wall. 



The internal suture (pi. IV, fig. 35) has been observed on a rela- 

 tively small specimen. The antisiphonal lobe is long, narrow and 

 funnel-shaped. The first lateral lobe is at least as broad as the anti- 

 siphonal one, and more than one-half deeper ; it is also funnel-shaped. 

 The second lateral lobe is funnel-shaped, broad, and only half as deep 

 as the first one. 



All the internal saddles are rounded at the top and tongue-shaped. 

 The internal saddle is only very little higher than the first lateral. The 

 second lateral saddle is much lower; one of its flanks is on the um- 

 bilical wall. 



Even the largest specimen found is septate throughout ; the complete 

 shell therefore would be much larger than our number i. 



Relation to other species: 



All the species of Schistoceras resemble each other externally very 

 much. The principal differences are found in the ratio of dimensions, 

 the figure of the cross-section and in the details of the suture. Sch. 

 diversecostatmn n. sp. differs from Sch. Smithi n. sp. principally by 

 its larger umbilicus and the more rounded flanks ; further, the saddles 

 of the suture are more slender and slightly constricted, the auxiliary 

 saddle is broader and entirely on the flank, while in the older species 

 it is j)artly on the umbilical wall. 



From Sch. Hyatti Smith^ it differs principally by its wider umbilicus 

 in the mature stage, while in the immature stages the umbilicus is 

 much wider in Sch. Hyatti. At a diameter of 42 mm. we find the ratio 

 between diameter and umbilicus in this latter species to be i :o.23, 

 while in one of ours (I) it is 1 10.24 ; in a specimen with a diameter of 

 21 mm. it is in Sell. Hyatti i :o.2'8, while in a specimen of ours with a 

 diameter of 16.7 mm. it is still 0.25; in a specimen of Sch. Hyatti 



'J. p. Smith, Carb. Amm. of North America, p. 108, pi. 20, fig. 1-8; pi. 21, fig. 10-13. 



