604 MR. H. F. BLANFORD ON THE DESCRIBED FORMS OF TANALIA. 



anomalous case of a very limited area inhabited by seYeral peculiar genera, each of which 

 is represented by a large number of species. 



During a late visit to the island, I enjoyed the opportunity of examining the rich local 

 collection of Major Skinner, a collection which, including a large number of specimens 

 of several of the peculiar species, afforded excellent data for determining how far the 

 numerous forms described by recent authors were really distinct species, or merely 

 varieties linked together by intermediate forms. Major Skinner informed me that, in the 

 case of two of the endemic genera {Aulopoma and Tanalia), he had found it impossible to 

 discover any constant association of characters by which one species could be satisfactorily 

 separated from another, and that many of the described species of Acliatina and certain 

 Helices presented difficulties of the same kind, increasing as he obtained collections from 

 a greater niunber of localities. Having myself, while collecting in Southern India, noticed 

 the great variability of certain species, and that in many cases, owing to the describers not 

 being provided with intermediate forms, varieties of the same shell had been described 

 imder different names (e. g. Helix fallaciosa, Ferussac, H. ruginosa, Ferussac, and H. crassi- 

 costata, Bens. ; H. Trcmquebarica, Pabricius, H. semirugata, Beck, and H. vitellina, Pfr.), 

 I addressed myself during my stay in Colombo mainly to the examination of such puzzHng 

 species, with a view to trace out the connexion of varieties by the comparison of a large 

 number of specimens, or to fix the limits of variation so far as the collection permitted. 

 How necessary such revision has become in the case of many of our Indian shells any one 

 who has collected over an extensive area, and endeavoured to trace out the geographic 

 range of species, will readily acknowledge. In a subsequent paper I purpose contributing 

 such corrections of Indian species as my own collections have enabled me to establish ; 

 in the meantime I give the results of my examination of the genus Tanalia, the numerous 

 described forms of which are all peciiliar to Ceylon. In another paper I shall submit a 

 similar notice of the Aulopomas and certain Cyclopliori *, Helices, and Aclmtinas. The 

 Melanias and Amjmllarias equally require revision ; but these must be considered m 

 connexion with Indian species, most of them having a very extensive range. 



Genus Paludomus. 



Subgenus Tanalia, Grai/. 



I have little to add to the description of this subgenus, given by Mr. Layard, except to 

 notice the variability of the form of the operculum. This appendage is sometimes broadly 

 triangular, the angles being more or .less rounded, sometimes compressly elliptical; and 

 the nucleus, usually about the centre of the dextral edge, or a little inferior, is, in one 

 species [or variety ?], T. violacea, Layard, at the dextral corner of the base, and sometimes 

 projecting below the basal edge. A monstrous form of the operculum (possibly that upon 

 which Mr. Layard founded the subgenus Ganga) is not infrequent : in this, the nucleus 



* Since the above was written, Mr. L. Reeve's Monograph of this genus has reached me, and 1 have had the satis- 

 faction of seeing that he has therein made many of those corrections in the described species, of the necessity of which 

 I had already convinced myself. 



