G. C. Crick — On VesUnautllus. 553 



■by minute transverse strise, which, cutting the former, impart 

 a beautifully crenulated appearance to this part of the shell as seen 

 under the lens. After the first whorl is passed the spiral lines 

 begin to widen, and those of the lower half of the whorl entirely 

 disappear, leaving five ridges, the two lower ones being very faint, 

 till finally they all become obsolete, leaving only the transverse lines. 

 These are regularly arranged and very numerous, their distance 

 apart in the adult shell being almost exactly 1mm. From the 

 appearance presented by one of the specimens it would seem that 

 they imbricate, but this is not very distinctly seen. They form 

 upon the peripheral area a very distinct and deep, backwardly- 

 directed sinus, indicating the presence of the hyponomic sinus of the 

 aperture. On each side of the peripheral area there are three or 

 four faint ridges in the young shell, but before the second whorl 

 has been reached they have entirely disappeared. In a large 

 individual in the senile stage of growth obscure folds and tubercles 

 are developed upon the peripheral area and in one or two places 

 upon its margin, but these are not sufficiently prominent to alter the 

 general features of the shell. 



" The septation is not known .... 



" The siphuucle is about twice its own diameter from the peripheral 

 margin. 



"The body-chamber is imperfect in the specimen in which it 

 ■ is seen .... 



" The test is rather thick, especially upon the umbilical border, 

 where it forms the thickened rim . . . ." 



In his remarks on the species the author says : " The question 

 of the generic affinities of this shell is a difficult one to settle iu 

 the absence of a sufficient number of specimens wherewith to study 

 the stages of growth from the very young to the old shell, and 

 their modifications. . . . It is unfortunate that the septation. 

 is not to be got at, as this would have aided very much in the 

 determination of the affinities of the fossil." 



The dimensions given of the largest specimen (which was 

 elliptical) known to the author are : — greatest diameter, 127 mm. ; 

 smallest diameter, 102 mm. ; height, from centre of area of inclusion 

 to centre of ventral ai'ea, 24 mm.; width, from the summit of one 

 umbilical rim to the summit of the other, 44 mm. 



Though exhibiting some differences from the figured example, 

 there is in the British Museum a specimen (No. C. 8861) which 

 in my opinion is referable to this species; and which, if correctly 

 identified, adds to our knowledge of the species by revealing to 

 some extent the form of the septal sutures ; unfortunately, the locality 

 whence the specimen was obtained has not been recorded. 



The latter half of the outer whorl of the fossil is very slightly 

 crushed, but the specimen is not otherwise distorted. The fossil 

 is 85 mm. in diameter ; it is entirely septate ; the body-chamber 

 is wanting, and a portion of the inner whorls is either absent or 

 obscured by the matrix which covers the central vacuity ; the outer 

 whorl and nearly a half of the penultimate whorl are clearly shown, 



