18 BRITISH FOSSILS. 



lamella, whence the cut surface presents concentric and radiating 

 structure lines. 



What the proper structure of the guard may be is more doubtful. 

 In all specimens I have examined the texture of the guard is dense 

 and thoroughly calcified, and any indications of structure are of a 

 crystalline and not an organic character. The guard of the specimen 

 longitudinally and vertically bisected, of which a diagram, twice the 

 natural size, is given in Plate III., fig. 3, presents a dark longitudinal 

 axial line, a dark terminal transverse line, and another less dark 

 transverse line rather above the middle of its length. 



The terminal transverse dark line is visible on the exterior of the 

 specimen, and looks at first like a colour band, a sort of indication 

 of the natural termination of the guard. But, on closer exami- 

 nation, these transverse markings are seen to arise merely from the 

 presence of plates of calcareous spar ; in other words, the calcareous 

 infiltration is transparent in these parts of the fossil. The dark axial 

 line appears to me to result from similar conditions. 



The internal shell just described has not yet been found associated 

 with ink-bag, hooks, or beaks. The peculiar form of the pro-ostracum, 

 the long narrow phragrnocone, and the cylindroidal guard, distinguish it 

 generically from all the other Belemnitidce. I, therefore, propose for 

 this new generic type the name of Xiphoteuthis, and retain for the 

 present, the only known species of the genus, De la Beche's term of 

 elongata. 



Is the guard entire in these specimens of Xiphoteuthis elongata, or 

 has its apex been broken off ? Was it originally solid and composed of 

 fibrous lamella?, or was it, like Belemnites tubularis, hollow through a 

 greater or less part of its extent ? The specimens which have passed 

 through my hands do not enable me to give a definite reply to these 

 questions. 



I suspect that a thoroughly well-preserved specimen of Belemno- 

 teuthis will some day demonstrate the existence of a fourth kind of 

 pro-ostracum among the Belemnitida?. Mr. Pearce, as we have already 

 seen, speaks of a " sepiostaire " in this genus ; .and Mr. Woodward 

 ascribes to it " a horny dorsal pen, with obscure lateral bands." 

 A specimen of Belemnoteuthis from the Oxford Clay, in the British 

 Museum (Plate II., fig. 2), shows very distinct traces of a pro-os- 

 tracum of this kind. The fossil is unfortunately much crushed, but 

 from one lip of the phragmocone there obviously proceeds the horny- 

 looking plate (a, a), the two lateral contours of which, obscurely defined 

 from the matrix, pass into one another at an acute angle at b. A 

 narrow band of horny-looking matter, marked by oblique stria?, is dis- 

 cernible at c, and is quite distinct from the remains of the mantle (/), 

 under which it seems to pass. 



Is the triangular plate part of the ventral pro-ostracum, and the band 

 c the remains of the dorsal portion of that structure ? I am inclined 

 to think so, though the .state of the fossil is not such as to encourage 

 positive assertion. 



It has been seen that at least two genera of Belcmnitida;, viz., 

 Belemnitcs and Belemnoteuthis, have hooks, arranged in double rows, 

 upon their arms. Now similar hooks, sometimes isolated, some- 



