422 Systematic Paleontology 



Family VOLUTIDAE 1 



Genus ROSTELLITES Conrad 

 [Proc. Acad. Nat. Sci., Phila., vol. vii, 1855, p. 268] 



Type. — Rostellites texanus Conrad. 



" Univalve, elongated, with an expanded labruin, and having numerous 

 oblique plaits on the columella." — Conrad, 1855. 



Dr. Dall, who has so ably monographed the Volutidce, differentiated the 

 genus as follows : 2 



" The genus Rostellites is characterized by a usually thick shell with 

 a tendency to cancellated sculpture of distant narrow ridges, more or less 

 nodose at the intersections; by an acute apex and trochoid, minute 

 nucleus; by a tendency to a notch or sulcus in the outer lip near the 

 suture; and by the presence of several well-differentiated plaits on the 

 pillar. A few species are thin and the form is extremely variable. The 

 surface is not glazed, the pillar is nearly straight, and the incremental 

 lines are conspicuous." 



The genus is world-wide in its distribution in the Cretaceous, but has 

 not been reported from the earlier Mesozoic nor from the Tertiary. 



A. External sculpture dominantly spiral; maximum diameter of shell 



approximately one-quarter of its altitude Rostellites nasutus 



B. External sculpture dominantly spiral; maximum diameter of shell 



more than one-quarter of its altitude. 



1. Altitude of adult shell exceeding 60 mm.; entire surface finely 



threaded spirally Rostellites marylandicus 



2. Altitude of adult shell not exceeding 60 mm.; external surface 



not finely threaded spirally ? Rostellites jamesburgensis 



Rostellites nasutus (Gabb) Meek 



Volutilithes nasuta Gabb, 1860, Jour. Acad. Nat. Sci., Phila., 2d ser., vol. 



iv, p. 300, pi. xlviii, fig. 9. 

 Fulguraria nasuta Gabb, 1862, Proc. Acad. Nat. Sci., Phila. for 1861, p. 364. 

 Rostellites nasuta Meek, 1864, Check List Inv. Fossils, N. A., Cret. and 



Jur., p. 21. 

 Rostellites nasutus Conrad, 1868, Cook's Geol. of New Jersey, p. 730. 



Etymology: Rostellum, diminutive of rostrum, beak; 7x77s, allied to. 



1 The representation of the Volutidm in the Maryland Upper Cretaceous is 

 curiously meager. The recent Volutes are among the characteristic deep- 

 water forms and it is probable that the absence of the group as a major factor 

 in the univalve fauna is indicative of unfavorable shallow-water conditions 

 under which the Matawan and Monmouth were laid down. 



2 Dall, 1890, Trans. Wagner Free Inst. Sci., Phila., vol. iii. pt. i, p. 72. 



