250 Mil. G. C. HOBSON ON THE 



to Semper (1870), a brief description by the same author of 

 C. granulata (Krauss), and a short account of some of the internal 

 parts of C. crawfordi (Morelet) due to Pilsbry (1904). 



II. Structural. 



1. Anatomy of Gochlitoma zebua (Brug.) var. obesa. 



Two specimens were available for dissection, both almost fully 

 grown and referable to Pfeiffer's variety obesa. They measure 

 83x47 mm. and 82x47 mm. respectively, and are thus a little 

 shorter than Pfeiffer's type (1854). In the following description 

 the two examples are referred to as z x and z 2 respectively. 



External Features. 



(1) Shell. — The conchological status and synonymy has been 

 discussed by Pilsbry (1904). It is necessary, however, to refer 

 in some detail to these features in order to show what relation 

 there is between the variation of external and internal characters. 



In Pilsbiy's description the columella is "arcuate." In z x it is 

 perfectly straight and contrasts strikingly with the arcuate form 

 seen in z . In z x there is a well-marked callus which is absent 

 in z.,. The coloration, invariably regarded as an inconstant 

 feature, is markedly different in the two forms. Z„ agrees with 

 Pilsbry's description, but in z 1 the dark stripes are often twice 

 and thrice the size of the white ones. Both examples have 7^ 

 whorls. The aperture varies. In z, it is wider and shorter 

 than that of z , measuring 48 x 27'5 mm. as compared with 

 50'5x26 mm. 



The sculpture is, as Pilsbry says, granoso-decussate. But in 

 both forms the spiral stria? are weak, so that, as a result, the 

 transverse ribbing is more marked than in the variety fulgurala. 

 In z. the spiral striation is stronger than in z,. This sculpture 

 starts at about half-way round the second whorl in z y and three 

 quarters of the way round the second whorl in z 2 . It is con- 

 tinued in botli cases to the end of the sixth whorl. A peculiar 

 character seen in the var. fulgurata as well, Adz. the enlargement 

 of some of the longitudinal bands of granules; is seen in a weak 

 condition in z , but is absent in z.,. There is, however, in the 

 same position an abrupt enlargement of all the granules. 



(2) Coloration. — This is more fully dealt with in Mrs. Long- 

 staff's paper. 



(3) Mantle-folds, etc. — The cervical lobe was thick, narrow, and 

 pointed in z x . That of z 2 differed only in being much longer. 

 The posterior lobe is irregular in shape and has two main sur- 

 faces, one vertical (between which and the cervical lobe the anal 

 canal runs) and one horizontal. The latter is continuous with 

 the shell-lobe. 



(4) Anus, etc. — The amis and pneumostome lie more or less 

 closely together. The latter is interior to and rather below the 



