ORTHAULAX, A TERTIARY GUIDE FOSSIL. 



31 



No other molluscan shells were found associateil with 

 this Onhaulax, but an echinoderm occurred. 



It is a little siu-prising that the nearest ally of this Porto 

 Rican Onhaulax should be not Gabb's 0. inornaius, from 

 the adjacent island of Santo Domingo and in the Tampa 

 and '\\Tute Beach beds, Florida, but 0. pugvux. The lat- 

 ter ranges geographically from the Tampa, Fla., beds and 

 those of Bainbridge, on the Flint River, Ga., to Oul>a, 

 Antigua, and the Canal Zone, and geologically from the 

 middle Oligocene of Antigua to the upper Oligocene of 

 the Tampa and Flint River formations. 



Orthaulax agnadillensis resembles 0. caepa in 

 size and appearance but differs from it in sev- 

 eral respects: 0. aguadiUenffis is blunter, the 

 apical angle being a little greater than 90°, 

 whereas that of 0. caepa is a little less than 90°; 

 some specimens of 0. aguadillensis show faint 

 grooves on the anterior part of the shell but 

 no raised tlireads such as are found on O. caepa: 

 most of the callus on 0. aguadillensis is depos- 

 ited just in front of the shoulder and is propor- 

 tionately somewhat thicker than in 0. caepa, 

 on which the callus is more evenly distributed 

 and is lunate in cross section. 



Localities: Aguadilla, P. R., station 3, Reeds, 

 collector; road from Cotui to Cevicos on 

 east side of Arroyo Blanco east of Loma de 

 los Palos, Dominican Republic, station 8.598, 

 Cooke and Ross, collectors, 1919; left bank of 

 Rio Yaque del Sur at upper edge of Los Guiros, 

 Province of Azua, Dominican Republic, sta- 

 tion 8.572, Condit, collector, 1919; west bank 

 of Rio Yaque del Sur opposite Palo Copado, 

 Province of Azua, Dominican Republic, station 

 8590, Condit, collector, 1919; Crocus Bay, 

 Anguilla, station 6965, Vaughan, collector 

 (identification doubtful). 



Geologic horizon: Aguadilla limestone, Cevi- 

 cos limestone, and Anguilla formation ( ?) , up- 

 per Oligocene; Yaque group ( ?), Miocene. 



Type: American Museum of Natural History. , 



Orthaulax caepa Cooke, n. sp. 



Plate V, figures 2a,~'ih. 



Onhaulax inornaius Cooke, Carnegie Inst. Washington 

 Pub. 291, p. 116, pi. 2, figs. 1, 2, 1919. 



Shell large, heavy, circular in cross section; 

 first six whorls, more or less, bare in juvenile 

 shell but completely enveloped by subsequent 

 whorls ; callus-filled spaces between whorls 

 evenly lunate in axial sections through the 

 apex; apex conical, with apical angle of about 

 85°, or hemispherical; whorl in front of the 

 shoulder ornamented with fine raised revolving 

 threads. 



Orthaulax caepa is intermediate in shape be- 

 tween <). inornatuH and 0. affuadiUensis. Its 

 apex is blunter than that of 0. inornatus but 

 more acute than that of 0. agitadillen.ns. It 

 differs from both in the ornamentation of 

 spiral threads in front of the shoulder. The 

 cast of the interior appears to be more slender 

 than that of either 0. inoi-nafus or 0. aguadil- 

 lensift, and the whorls of the cast to be more 

 rounded than those of 0. inornatus but very 

 similar to those of 0. aguadillensis. The callus 

 in 0. caepa is evenly lunate, but that of 0. 

 aguadillensis is asymmetric, the greatest thick- 

 ness being in front of the shoulder, and is much 

 thicker in proportion to its length than that of 

 0. caepa; the callus is thin and inconspicuous 

 in 0. inornatns. 



There are two forms of <). caepa, a pointed 

 or conical form and a domed or hemispherical 

 form. It is possible that these different shapes 

 may be secondary sexual characteristics. 



Locality: Consohicion del Sur, Pinar del 

 Rio, Cuba, station .3474. 



Geologic horizon : Oligocene (?). 



Type: U. S. Nat. Mus. catalogue No. 166980. 



