INSTITUTE OF SCIENCE, PHILADELPHIA. 297 



Genus C^CUM Fleming. 



Comparatively few species of this genus have been described from the 

 American Tertiary. 



In the Miocene we have C. virginiamim Meyer and C. Stevensoni 

 Meyer, from Yorktown, Va. (Proc. Am. Phil. Soc. xxv., No. 127, p. 

 139, figs. 3 and 4, 1888). Specimens collected at Yorktown by Mr. Harris in- 

 dicate that these two species are valid. C. annulatnni Emmons {iion Brown), 

 from the Newer Miocene of North Carolina, is C . floridanuin Stimpson ; C. 

 annulatiim Gabb (Geol. St. Domingo, 1873, p. 241 ; Journ. Acad. Nat. Sci., 

 2d Series, viii. p. 363, pi. 46, fig. 59, 1874), non Brown nee Emmons, appears 

 to be a good species, but the figured type seems to be the second stage of 

 what in the adult condition Gabb has named and figured [op. cit. f. 58) as C. 

 crassicostum, which name, as anmtlatiun is preoccupied, may be kept for the 

 species. The original form came from the Miocene of Santo Domingo and the 

 adult from the Pliocene of Costa Rica. We have no very similar species in 

 the Tertiary of the United States, though a not quite adult C. floridanum 

 would approach it. C. constrichiin Gabb (Geol. St. Domingo, p. 241, 1873) is 

 with little doubt identical with Meioceras nitidum Stm. The other species 

 known from the American Tertiary will be found referred to below. 



Caecum solitarium Meyer. 



C. solitaritmi Meyer, Ala. Geol. Rep., p. 68, pi. iii. fig. 9, 1886. 

 ? C. alterum Meyer, Ber. Senck. Nat. Ge?. 1886, p. 6, pi. i. fig. 8. 



Eocene of Vicksburg, Miss., Meyer ; Orthaulax bed at Ballast Point, 

 Tampa Bay, one specimen, Dall. 



C. solitarium is described as smooth except for incremental lines, and 

 figured as 2 mm. long. A typical specimen named by Meyer is 2.6 mm. long 

 and is in the second stage of growth. The enlarged beginning of the third 

 stage is present and shows distinct but not prominent annulse ; in the adult 

 condition this species is doubtless one of the annulate forms. The specimen 

 from the silex-beds is too imperfect to be positive, but looks as if it might be 

 an incomplete example of the second stage of the same shell. 



The plug is bluntly conical, with the apex nearest the right side of the 

 posterior aperture. 



C. alterum Meyer, also from the Eocene of Mississippi, at Jackson, may 

 well be the third or adult stage of C. solitarium. It is represented as annu- 

 late, without any expanded lip, and 2.5 mm. in length. These two forms, if 

 they be more than diverse stages of a single species, are, so far as yet known, 

 the only American Eocene species of the genus. 



