500 BULLETIN 10 0, UNITED STATES NATIONAL MUSEUM 



I also have before me four specimens (U.S.N.M. no. 313655) col- 

 lected by Pedro de Mesa at Calawagan, Paluan, Mindoro. These are 

 in every way darker than the others but may belong here. More 

 material, however, will decide the fate of this element. 



The shells that have been listed under the name Cochlostyla min- 

 doroensis (Broderip) belong to two phylogenetic stocks as evidenced by 

 the color of their nuclear whorls, which are embryonic features. In 

 one group we have a soiled-white tip ; in the other, a purplish-brown tip. 



Before adequate material was at hand I believed that we might be 

 dealing with a hybrid mutating complex, resulting in the many forms 

 that the island presents, but the constancy of the color of the nucleus, 

 combined with equally constant sculptural characters and general 

 color pattern in the material gathered from certain areas, convinces 

 me that this is not the case. For any other groups, such as Cerion, 

 where I have found hybridization to be the source of mutation where 

 different colored embryonic whorls were present, the progeny showed 

 those characters, that is, white or buff tipped in the offspring, without 

 any relation to the rest of the shell characters; in other words, a light 

 tip, let us say, a character of Species A, would appear on a shell having 

 all the rest of the characters of the other pattern Species B, which has 

 a buff tip, the color of the nucleus only indicating the relationship to 

 Species A. 



No such mix-ups are present here, and if the many forms of the 

 variegated Cochlostylas of Mindoro are the product of hybridization, 

 then this must have taken place so long ago that complete segregation 

 and fixation have taken place. 



We have a similar situation presented in Amphidromus in southern 

 Palawan and the adjacent small islands of that region, where Amphi- 

 dromus quadrasi and its races always have a white tip in their colony 

 regardless of the other color features, and Amphidromus versicolor in 

 all its races has a dark apex. Among thousands of specimens examined 

 of these two species I have been unable to detect an exception. Each 

 colony usually occupies a distinct island or, in the case of the large 

 island Palawan, a distinct portion of it, and all its members definitely 

 align themselves with one or the other species. 



It is my firm belief that the Mindoro Cochlostylas present a similar 

 state of affairs and that in the past naturalists lumped shells of a 

 general resemblance in the catch-all Cochlostyla mindoroensis because 

 they had insufficient material without definite locality labels as typified 

 by the old collections in the National Museum. An examination of a 

 large series of specimens from a given locality will show that they 

 definitely belong to the light- or dark-tipped forms. A separation on 

 this basis makes it easily possible to trace these over the island where 

 each group breaks up into zoogeographic races. 



