li)06.] NATURAL SCIENCES OF PHILADELPHIA. 57 



The tubercles are a little sharp, and the protruded mantle shows a 

 very slight tendency to smooth the preceding whorl — a tendency which 

 in later forms results in a senile feature. 



Remarks. — This form possesses no stage later than the cancellated 

 stage and never has a shoulder angle. The suture tubercle is through- 

 out life the dominant one. The specimens are remarkably uniform, 

 no perceptible individual variation occurring. The smooth stage is 

 very long. From its primitive characteristics, and its geological posi- 

 tion near the base of the Eocene, the wTiter has no hesitation in assign- 

 ing to it an ancestral position among the races and species dealt with 

 in this paper. 



Fig. 3. — Volutilithes rugatus Conrad. Matthew's I>anding, Ala. Adult indi- 

 vidual. Length = 44 mm. 



Volutilithes rugatus Conrad. 



Locality — Matthew's Landing, Ala. 



This species was originally described by Conrad as Volutilithes 

 rugata in Jour. Acad. Nat. Sci. Phila., 2d Series, Vol. IV, p. 292, PI, 

 47, fig. 32. 



Whorls 1,2, 3 — Smooth and rounded. 



Whorl 4 — Smooth and rounded, except near the end, where in many 

 individuals the ciu'ved rib stage begins. 



Whorl 5 — The curved rib stage usually occupies the latter part of 

 four and early part of five. Its ribs are wide apart and it persists for 

 about a quarter of a whorl. It is followed by the straight, tubercled 

 ribs of the cancellated stage. The two upper tubercles are the largest, 

 those below becoming fainter anteriorly. The ribs die away anteriorly 

 on the branchial siphon. Each tubercle is connected with the corre- 

 sponding one of the next whorl by a spiral. 



