1«S(S COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bttll.106. 



Aperture transversely reniform or sublimate. Surface ornamented by 

 rather small, regular, rounded costse, which pass nearly straight across 

 the sides of the whorls, and arch slightly forward in crossing over the 

 periphery, on which from thirty-six to forty of them may be counted to 

 every turn; each of those commencing at the umbilicus, usually there 

 a Little enlarged, especially on the larger whorls, so as to form a small 

 subnodose prominence. Beyond these they all (particularly on the 

 inner whorls) bifurcate regularly once, near the middle of each side, 

 and on the larger turns others are also intercalated between, so as to 

 make the number on the peripheral side five or six times as great as 

 at the umbilicus. 



"The septa are rather crowded, and provided with branched and 

 deeply sinuous lobes and sinuses. The siphonal lobe is about one-fourth 

 longer than wide, nearly obovate in form, and ornamented with three 

 principal branches- on each side, the two terminal of which are larger 

 than the others, and each provided on the outer side with two or three 

 more or less digitate lateral branchlets, while the inner parallel mar 

 gins are merely sharply serrated. The first lateral sinus is of about 

 the same size as the siphonal lobe, a little Oblique, nearly oblong in 

 form, and divided at the extremity into two tripartite and obtusely 

 digitate branches, of which the one on the outer side is larger than the 

 other; behind these it is provided on each side with two alternating 

 lateral branches with sinuous margins. The first lateral lobe is nar- 

 rower and shorter than the siphonal lobe, and provided with two prin- 

 cipal branches on each side, the two terminal of which are much larger 

 than the others, and of unequal size, the one on the right or peripheral 

 side being the larger. Both of these terminal brandies are distinctly 

 bipartite, the subdivisions being ornamented with several branchlets 

 and smaller digitations. The second lateral sinus is about half as wide 

 and nearly two-thirds as long as the first, more or less oblique, and 

 rather deeply divided at the extremity into two subequal, bifurcating, 

 and obtusely digitate terminal branches. The second lateral lobe is as 

 long as the second lateral sinus, but a little narrower, and ornamented 

 with three variously digitate terminal branches, the middle one of 

 which is Longer than the others, a little oblique, and not exactly ecu 

 tral. The third lateral lobe is small, being less than half as long, and 

 scarcely two thirds as wide as the second lateral, and provided with 

 three nearly equal, spreading, digitate, terminal branches. Between 

 the third lateral lobe and the umbilical margin there are two other 

 small, very unequal, lateral lobes, the first of which has two or three 

 digitations on each side, while the second is nearly simple or but 

 slightly sinuous on the margins." 



The only examples of this species I have seen are the types, consist 

 ingof the specimen figured and a septate fragment of a much larger 

 individual. As the body chamber is lacking these do not show whether 

 the Species had its last volution deflected and separated from the rest 

 of the shell, still it s apparent ly close relationship with J$C(iphite8 ven- 





