OWEN ON THE BELEMNITE. 123 



sanguiferous vessels, it must have equalled in thickness that of a 

 Calaniary of the same size ; and this indeed is evident, since the 

 mantle of true Calamaries with horny pens ( Teuthidce) preserved 

 in the same matrix is reduced to a compact fibrous layer of the 

 same thinness. 



The specimen now alluded to (Mr. Pratt's) is chiefly remarkable 

 and valuable for the perfect conservation of the complex muscular 

 structures of the head and its uncinated arms. Eight of these latter, 

 forming the normal series of cephalic arms, may be defined, radi- 

 ating from a contracted base. In this base may be observed two 

 decussating groups of curved fibres ; the posterior one, with its 

 concavity turned towards the mantle ; the anterior one, with its 

 concavity directed forwards, and its horns continued into the bases 

 of the arms. A similar decussated arrangement of fibres exists in 

 the Onychoteuthis, and is described and figured by Cuvier in the 

 corresponding part of the head of Octopus. 



Almost the whole extent of five of the cephalic arms is pre- 

 served ; they are rather longer, in comparison with the mantle, 

 than in the modern Onychoteuthis, but not as compared with the 

 entire body of the Belemnite, when this is lengthened out by the 

 terminal guard : the longitudinal arrangement of the fasciculi of 

 muscular fibres of the arms is very distinct. 



Each of the arms seems to have been provided with from fifteen 

 to twenty pairs of hooks, which were doubtless developed from the 

 horny hoops which encircled the caruncles of the acetabula, as in 

 the modern Onychoteuthis. 



Two small protuberances at the origin of the normal brachia are 

 the only parts which represent the bases of the pair of long ten- 

 tacula superadded to the eight shorter arms of the existing 

 Decapoda. 



On each side of the head, behind the bases of the arms, there is 

 a convex protuberance formed by a well-defined semicircular band, 

 about a line in thickness, of grey fibrous matter, the fibres or layers 

 being parallel with the curve of the band. In another specimen 

 these parts are regularly placed in reference to each other, being 

 on the same transverse line, with their concavities towards each 

 other, and their convexities turned outwards : each body is a line 

 in breadth, and does not diminish at either extremity, which is lost 

 in, or hidden by, the surrounding muscular tissue ; their structure 

 is more minutely, but more definitively, fibrous than in the muscles, 

 the fibres following the curve of the band. The parts in existing 

 Cephalopods, which first suggest themselves for comparison with 

 these, are the beak, the cartilage of the head, the cornea, or the 

 crystalline lens. The position of the curved fibrous bodies is pos- 

 terior to that in which the beak should be placed agreeably to exist- 

 ing analogies ; the texture of the beak also in Onychoteuthis is the 

 same as that of the hooks, whilst the texture of the parts in question 

 is very different from the black horny matter of the preserved 

 hooks. The position of the parts corresponds with that of large 

 sessile eyes, only that they are more nearly approximated towards 



