118 PEOCEEDIXGS OF THE MALACOLOGICAL SOCIETY. 



undoiibtedly derived from the ink-bag, the side next the stain is 

 considered to be the inner or ventral surface, and it is this surface 

 which is Tvell displayed on the slab marked A, and to which the 

 following description chiefly applies. 



The anterior portion of the phragmocone exhibits the broken edges 

 of one or two of the septa, the anterior border being about 1mm. in 

 advance of the last septum, which was apparently incomplete. The 

 phragmocone is of a brownish colour, while the procistracum is much 

 thinner, nearly white, and forms a layer external to the phragmocone. 

 The anterior boundary of the latter is not distinctly marked ; it is, as 

 it were, spread over the proustracum ; and that it was a layer distinct 

 from the latter, seems evident from the fact that the central rib of 

 the proostracum arises quite suddenly, as if it came up behind the 

 phragmocone. 



The proostracum is a broad, spatuliform plate, of about the 

 thickness of a piece of writing-paper, about four times as long as 

 broad, somewhat contracted posteriorly, and somewhat expanded 

 anteriorly. It is not possible to give the exact diameter of the 

 anterior part of the phragmocone, but in its crushed condition 

 its width is about 25-5 mm. The posterior part of the proostracum is 

 19mm. wide (about three-quarters of an inch); its length is 74mm. 

 (or rather more than 2-|- inches). Passing forwards from the anterior 

 border of the phragmocone, it contracts slightly, so that at about 

 16mm. from the border of the phragmocone it is only 17mm. wide; 

 thence expanding gradually, it attains its greatest width, viz. 23 mm., 

 at about 5 mm. from the anterior extremity ; it then narrows very 

 rapidly, its antero lateral boundaries being somewhat flattened, or 

 even slightly concave. A small portion of the central part of the 

 anterior extremity is wanting in the specimen, so that there appears 

 to be a notch here in the median line : this may be accidental, 

 and the anterior boundary may originally have been rounded and 

 entire. 



The proostracum is bounded on either side by a longitudinally 

 striated band, which is rather thicker than the rest of the proostracum 

 and is continued over the surface of the phragmocone, the impression 

 of the longitudinal strife being seen in one or two places where the 

 phragmocone has been broken away. The outer boundary of each 

 band is also thickened. At the anterior part of the phragmocone 

 these bands (the dorsal processes of Mantell) are each 5 mm. wide ; 

 they gradually become narrower anteriorly, and disappear at the 

 antero -lateral angles. 



The median line of the proostracum is occupied by a narrow, hollow 

 rib, about 0'5 mm. wide, convex venti'ally, and bearing a very narrow 

 median groove. This central rib can be traced from the anterior 

 border of the phragmocone, and is seen gradually to become wider and 

 less distinct towards the anterior end of the proostracum. 



A narrow portion of the proostracum on either side of the median 

 rib is longitudinally striated ; the rest of the area on each side is 

 marked by lines which curve xapwards and outwards. 



As to the homologies of the Belemnite shell with the sepion, or 



