BucHicEKAs (Sphenodiscus) Belviderenbis. 31 



Var. MENTORIANUS. 

 Plate I, fips. Hand 7. 



This variety is distiiiijjuisliod by having the two simple, 

 truncate saddles second and third exterior to that which is 

 in the course of the circuni-unibilical tubercles, remarkably 

 broad and shallow. The type is from the Mentor beds, near 

 Brookville, Kansas. 



Var. SERrENTlNUS. 

 Plate II, figs. 4-0. 



A'enter of entire body-chamber strongly and rather nar- 

 rowly rounded and sinuous, the convexities of the sinuosity 

 being correlated with pronounced, rounded or somewhat sud- 

 denly tlattish-crested ribs on the outer part of the body- 

 chamber, the tubercles seen on the ventro-lateral margin of 

 typical belriderensis being nearly lost in the ventro-lateral 

 shoulders of the ribs; the ribs separated by broadly round- 

 bottomed valleys of about their own breadth, and disai^pear- 

 ing about midway between the venter and the umbilicus; a 

 series of obliquely compressed tubercles encircling the um- 

 bilicus. Of the septate portion of the shell, only the anterior 

 part has well-developed ribs and tubercles, and a distinctly 

 sinuous and rounded venter, the posterior part of the venter 

 being abruptly truncate, as in typical belviderensis. 



This sub-species is common in and characteristic of the 

 Denison division, though its occasional occurrence in the 

 AVashita division also is probable. The types are from the 

 Pawpaw clays near Denison. 



