78 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



specialised form of the group (I have already pointed out its close affinities with 

 T.forniosiun), having a broad, elevated, median ventral (peripheral) zone. This 

 feature is strongly characteristic of Vestinautilus, though it is not shared in by 

 all the species of that genus — V. KonincJcii, A. d'Orbigny, V. cariniformis, A. 

 Hyatt, e. f/., having a concave peripheral area, just as T. Meyerianum has, contrary 

 to its congeners T. serratum, T. consobrinum, and T. intermedium, a convex one. 

 Localities. — Lisbane, county of Limerick; Garrihies, county of Kerry. 



Genus Vestinautilus, Bi/ckholt, 1852 (emend. Hyatt, 1883, 1893). 

 Vestinautilus semiglabek, sp. nov. Plate XXII, figs. 3, 4 a, b, c. 



Description. — Shell somewhat thick-discoid, consisting of about four volu- 

 tions, deeply umbilicated, with a small central vacuity. The whorls increase 

 rapidly in diameter, their section is subhexagonal. The ventral area is broad and 

 slightly arched, the sides are flattened, and are only slightly inclined inwards, the 

 edge of the umbilicus is subangular, its walls sloping towards the centre, thus 

 forming an obtuse angle with the sides ; the zone of impression is shallowly 

 concave with an acute edge. The whorls in the young shell are, as usual, some- 

 what rounded, and do not assume the angular form of the sides until after the 

 first whorl has been reached. The body-chamber (not quite complete anteriorly 

 in the only specimen which shows it) occupies perhaps rather more than half a 

 volution. It increases very rapidly in diameter, the width at the base of the cast 

 being about 25 ram., measured across the ventral area; that at the apertural 

 extremity being about 35 mm. in the same relative position. 



The margin of the ventral area, as seen in the cast, projects outwards on each 

 side of the body-chamber, in the vicinity of the aperture ; a sensible contraction 

 taking place in front of the projections, and a marked thickening of the test, 

 causing an elevation in its surface, is seen just below the cast of one of these 

 projections on the angular border of the umbilicus. 



The zone of impression is shallowly concave, and bordered on each side by a 

 prominent keel; within the keels there are two fine incised lines caused by the 

 ridges on the periphery of the whorl embraced ; the lines of growth upon the 

 latter are also distinctly reproduced. 



The septation in this species cannot be completely described, as it is only seen 

 imperfectly in the adult; the sutures are 6 mm. apart in the last two septa; in 

 the young shell the septa are 2'5 mm. apart where the diameter of the whorl, as 

 nearly as can be made out, is about 5*5 mm. The siphuncle is not seen. 



The ornamentation is both strongly marked and very beautiful. It consists 



