MUSEUM OF COMPARATIVE ZOOLOGY. 173 



valley, while P. globosa Pse. Mss. = Hebe var. will be found in a remote 

 valley. P. hyalina Brod. and P. faba Mart, range through all parts of 

 the islands where they occur. The island of Bora-bora, eighteen or 

 twenty miles northwest from Raiatea, should, from its size as compared 

 with other islands, produce five or six species. On the contrary, it pro- 

 duces but a solitary species, P. lutea Less., which is remarkably uniform 

 in its specific character, and widely distributed over the island. P. hya- 

 lina Brod. has the widest range of any other species inhabiting the Poly- 

 nesian Islands ; it has spread over Tahiti, and is abundant at the Austral 

 group, over three hundred miles south of the former island. It is also 

 found at Mangaia, one of Cook's Islands, five hundred miles southwest of 

 Tahiti. The Polynesian group, in which the greatest number of species 

 occurs, comprises eight islands, six of which are inhabited by more than 

 half of the known species of the genus. The distance of these islands 

 from each other is from ten to ninety miles. The former distance is 

 between Tahiti and Moorea, and the latter separates Moorea from Hua- 

 heine. Tahaa and Huaheine are only three or four miles apart, but 

 are enclosed in the same encircling reef, and may be regarded as one 

 island separated into two by more or less shallow water. Tahaa is in- 

 habited by two or three species comprising two or three distinct types, 

 which are also represented on Raiatea, but not elsewhere. Bora-bora is 

 ten miles from Tahaa, and, as before mentioned, possesses but a Bingle 

 species. Notwithstanding the short distance between the several islands, 

 and the constant intercourse of the inhabitants for hundreds of years, 

 not a single instance has come to my knowledge of a species bavin- 

 been introduced from one island to another." * 



Hybrids are common amongst some species, and rare with others. 

 They even occur between arboreal and ground species. As to the 

 amount of fertility existing amongst hybrids, we possess no certain 

 data, but to these intermediate forms is to be ascribed the embarrass- 

 ment which so often besets the conchologist in the determination of 

 species. As was to be expected, the hybrids in my oollection are 

 chiefly the result of the union of proximate species. I possess three which 

 partake of the mingled characters of P. orassilabris Pse. and P. bella 

 Pse. Mss. = Hebe var. ; one between P. affinia Pse. and P. rubea- 

 cens Etve. = Otaheitana var. \ two between P. radiata Pse. Mss. and 

 P. faba Mart.; several between I'. virginea Pse, Mss. and P. amanda 

 Garr. Mss. = faba var. ; three between P. virginea Pse. and P. dubia 

 Chirr. Mss.; two between P. virginea Pae. Bdss. and P. dentiiera IV., 



• Garrett in litt. 



