ON THE MOLLUSCAN GENUS COCHLITOMA. 249 



15. On the Molluscan genus Coclditoma and its Anatomy, 

 with Remarks upon the Variation of two close! v-allied 

 Forms. By G. <J. Robson, 13. A.* 



[Received December 10, 1920 : Read March 22, 1921.] 



(O.t'ered for Publication by permission of the Trustees of the British Museum.) 



(Text-figures 1-9.) 



Contents. 



Page 

 I. Introduction 249 



II. Structural : Anatomy of Coclditoma zebra var. obesa and fulgurata. 250 



III. Genetic Affinities and Variation of var. obesa and fulgurata 263 



IV. On the Classification of the Achatinince 264 



I. Introduction. 



In 1914 Mrs. G. B. Longstaff' brought from South Africa to 

 England some living examples of the big land-snails usually 

 referred to the genus Achat ma. A series of observations was 

 planned by herself and the author upon the habits and later 

 development of these forms. These observations were started 

 early in 1915, and, thanks to the satisfactory way in which the 

 animals acclimatized themselves, have been successfully continued 

 and some interesting results obtained which are given elsewhere 

 (infra, p. 379). As certain phases of the behaviour of the two 

 forms represented differed rather sharply and as their specific and 

 generic position was uncertain, an examination of their anatomy 

 was undertaken by the author. The principal object of this 

 paper is to provide additional knowledge of the anatomy of the 

 Achatinince; but it also affords an opportunity for discussing how 

 far the individuals of two closely -allied forms agree or differ in 

 all the details of their structure. 



The material for this study was presented by Mrs. Longstaff 

 to the Zoological Department of the British Museum (Natural 

 History) ; and the author is indebted to Mrs. Longstaff', and to 

 Major M. Connolly for information accessory to the study. 



The genus Cochlitoma was established by Ferussac (1821) for 

 a heterogeneous body of forms mostly referable to Achatina (s.s.). 

 The name was restricted by Pilsbry (1904) to a small group of 

 the Achatinince. Some thirty-five species were enumerated by 

 Pilsbry, and no substantial modification of the genus has been 

 made since. The group is restricted to S.E. and S. Africa though a 

 few forms straggle up the West Coast, and one species is apparently 

 erroneously recorded from Brazil. Our knowledge of the anatomy 

 consists of a very brief description of the late embryo and embry- 

 onic shell, shell-lobes, kidney, jaw, and genitalia of C. zebra, due 



* Communicated by Dr. W. T. Calman, F.Z.S 



