INSTITUTE OF SCIENCE, PHILADELPHIA. 295 



extending from the suture to the periphery, where they cease abruptly, the 

 interspaces wider than the ribs; lines of growth well marked; spiral sculpt- 

 ure of (on the last whorl seven above and seven below the periphery) 

 strong equal rounded threads with wider regular interspaces in which run 

 minute spiral striae ; whorls full, subangulate at the periphery, the base 

 slightly flattened ; suture distinct ; umbilicus pervious, bounded by a rather 

 wide smooth fasciole ; aperture subquadrate, sharply Urate inside ; a thin cal- 

 lus on the body; pillar thin, short, with a broad, sharp, nearly horizontal 

 tooth at the base. Alt. 9.0; max. diam. 8.0 mm. 



A single specimen of this well-marked little species was obtained. It 

 has the same pointed spire as the other Chipola species, but differs from 

 them and from the other American species in the details of its sculpture. 



Modulus floridanus Conrad. 



Moduhis floridanus Conr., Am. Jour. Conch, v. p. 107, pi. 12, fig. 6, 1870. 



Modulus corriigatui Stimpson MS. 



Modulus J^reisn Movch , Mai. Bl. x.xiii. p. 129, 1876. 



Pliocene of the Caloosahatchie beds, Dall and Willcox; Post- Pliocene 

 of North Creek, Florida, Willco.x; living on the west coast of Florida, the 

 Keys, and in the Antilles, and northward twenty-five to thirly-five miles off 

 shore to the latitude of Hatteras, North Carolina; also at Bermuda. 



Modulus modulus Linnd. 



Trochus modulus Linn^, Syst. Nat., Ed. x. p. 757, 1758. 



Trochus filosus Helb. -|- T. tectum Gmelin, -|- T. perlatus'OlWfi., -}- T. unidens March ; 

 Monodonta carchedonius Lam., -\- Modulus canaliculatus Beck, -|- M. lenticularis Auct. 



Pliocene of the Caloosahatchie and Shell Creek, Dall and Willcox ; liv- 

 ing from the west coast of Florida south to the Brazilian coast between tides. 



This ancient, well-known and e.xtremely variable species, of which M. 

 floridanus is. merely a race, is rather rare in the marls and seldom attains 

 the maximum size of recent specimens. 



Family C^CID^. 



The singular mollusks of this family have been monographed by Car- 

 penter and their classification reviewed by De Folin (Bayonne, 1875), who 

 has also printed a catalogue of the species. Owing to the remarkably dif- 

 ferent aspect these forms assume at different stages of growth in the same 

 individual, they are particularly well adapted to lead the unwary into error. 

 In the American Tertiary they extend from Mid-Eocene to the present epoch. 

 The group comprises five genera — CcBcum Fleming (1817), Meioceras and 

 Strebloceras Cpr. (1858), Parastrophia De Folin (1869), and Watsonia De 

 Folin (1879). 



In Cczcum the shell begins as a planorbiform nucleus, resembling a minute 

 Adeorbis, which is coiled symmetrically like a nautilus shell, from which the 



