PHRAGMOCERAS. HI 



IV. Family. — Pheagmoceratid^. 

 1. Genus. — Phragmoceeas, Broderip, 1839. 



The shell in this genus is more or less arched, and is in general laterally 

 compressed. The body-chamber is very large. The siphuncle is generally near the 

 concave side, which therefore must be regarded as ventral. The surface of the shell 

 has fine transverse markings. The mouth is very much constricted, the aperture 

 being very narrow and of a complicated key-like shape, very similar to that of 

 Gomphoceras, from which it is distinguished by its recurved form and the different 

 situation of the siphuncle. It belongs chiefly to the Upper Silurian, but several 

 typical forms occur in Barrande's Etage G, which belongs to the Devonian Age. 



As the specimens of Cephalopods from the localities whose fossils we are now 

 describing rarely retain the oral parts, it is extremely difficult to decide to what 

 genus some of the species belong. This is the case in the present instance, where 

 a single species appears to approximate the characters of the present genus, 

 though from the sliglitness of its arching and other qualities it appears to be a 

 somewhat aberrant form of it. In no case is the mouth of this species actually 

 seen. There appears to be a considerable amount of constriction round the upper 

 border, but it is quite doubtful whether this went on in the missing portions so 

 far as to form such an aperture as is characteristic of Phragmoceras. As, however, 

 the indications seem in favour of its having done so I have placed it provisionally 

 under this genus. 



1. Phragmoceras ? ungulatum, Whidhorne. PI. XI, figs. 5 — 8. 



1889. Pheagmoceeas ungulatum, Whidborne. G-eol. Mag., dec. 3, vol. vi, p. 29. 



Description. — Shell recurved, pyriform, rapidly tapering. Dorsal outline 

 nearly evenly convex, the convexity being considerable and increasing rapidly at 

 the summit. Lateral outlines not very oblique. Ventral outline rather convex on 

 the body-chamber, but becoming very concave in the septal part. Chambers 

 apparently rather deep. Section near the apical extremity circular, near the oral 

 extremity subquadrate. Aperture contracted considerably but defective in all the 

 specimens. Siphuncle unseen. 



Ornamentation consisting of multitudinous minute parallel transverse striae 

 or growth-lines which are slightly deflected over the median line. 

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