50 PROCEEDINGS OF THE ACADEMY OF [Vol. LXXIV 



In this group, the radulae of H. caracolla Moricand (1836) 26 

 and that of H. rhynchostoma ernesti von Martens 27 have been 

 examined. The formulae are given in Table III, and I expect to 

 study the group more thoroughly in the near future, as I have many 

 specimens from the Cumbres Mts., and Aroa Valley, Venezuela. 



The radula of this group like the shell-characters, are more or 

 less transitional between Oxyrhombus and Tristramia s. s. The 

 A-central has a heavy cutting edge, which is without cusps in the 

 specimen of ernesti examined, but usually bears one or two heavy, 

 irregular points in caracolla. The C-central has two large, rounded, 

 hook-like points and in caracolla has one or two minor points in 

 addition. The single Central American species appears closest 

 to H. rhynchostoma "Sh." Pfr. (1865), but also resembles con- 

 siderably H. rostrata Morelet, as pointed out by Crosse (1863). 



Section Tenuis A. J. W. Mexico to Central America; South America. 



Tenuis A. J. W. (1910). Type (by tautonomy) H. tenuis Pfr. (1849). 

 Mexico. 

 H. tenuis tenuis Pfeiffer (1849). Yucatan. Mexico. 



H. vernalis Mo. (1849). Peten, Guatemala. 



H. lindeni Pfr. (1849). Tapinapa, Mexico. 



H. chiapensis Pfr. (1856). Chiapa, Chiapas, Mexico. 



H. lindeni minor Ancey (1886) Honduras. 



H. lindeni ver apazensis A. J. W. (1905). Vera Paz, Guatemala. 

 ?H. tenuis pittieri A. J. W T . (1910). Rio de los Plutimales, Golfe Dolce, Costa Rica. 

 ??H. senachuensis A. J. W. (1910). Senachu, Guatemala. 

 H. delicatula delicatula Sh. (1852). Cordova, Mex. 



//. heloisae "Salle" Pfr. (1856). Cordova, Mexico. 

 H. delicatula notata "Salle" Pfr. (1856). Cordova, Mex. 

 ?H. durangoana durangoana Mousson (1883). Durango, Mex. 

 ?H. durangoana sagulensis A. J. W. (1910). Jalisco, Mex. 



The radula of the type species 23 was examined, and the radular 

 formula is given in Table III. It differs from that of H. zephyrina 

 by the presence of 4 small cusplets on the C-central, but agrees 

 with it in the lack of cusps and the development of the thickened 

 cutting edge of the A-central (Plate III, fig. 7; Plate IV fig. 14). 

 The cusps of the marginals are not arranged as completely on the 

 tip of the tooth as in H. zephyrina. 



Section Tristramia s. s. Mexico to Colombia. 

 Tristramia Crosse (1863). Type (monotype) H. salvini Tristram (1861). 

 Guatemala. 



!6 2 dried specimens A. N. S. P. no. 14622; collected in Brazil, by J. C. Anthony. 



27 1 alcoholic specimen; collected for the Univ. of Mich. Museum, at Palma 

 Sola, Estado Falcon, Venezuela (1920). 



28 4 specimens; University of Mich.- Walker Expedition to Southern Vera 

 Cruz, Mexico; Hacienda Cuatotolapam, Canton Acayucan. 



