88 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



The siplmncle, as seen in a polished section (PI. XXIV, fig. 3) and in a 

 distorted specimen from Little Island, is situated about its own diameter above 

 the centre, its position remaining tolerably constant throughout the entire growth 

 of the shell. 



The surface of the test has hitherto been described as smooth, but a specimen 

 from St. Doulagh's, in which the test is in a remarkably perfect state of preserva- 

 tion, shows a series of fine but very distinct longitudinal strige covering it (cf. de 

 Kon., ' Oalc. Garb.,' pi. xxviii, fig. 3 d). These are indistinctly seen on another 

 specimen with the aid of a lens ; they would probably have escaped my observa- 

 tion had not their presence in the first-named specimen led me to make a careful 

 search on others for similar markings. Crossing the keels bordering and within 

 the umbilicus there is, at regular intervals, a series of minute but very distinct 

 crenulations caused by a thickening of the lines of growth. 



'file perfect smoothness of the surface of the test — that is, the total absence of 

 any markings, even of the most minute description — in most of these fossils is 

 probably due to mineral action, which, in the slow process of fossilisation, com- 

 pletely replaced the original substance of the shell by calcite or by some form of 

 that mineral (perhaps aragonite), obliterating all but the coarser markings. That 

 this was not always the case, however, we see proofs in the presence of the 

 minute surface markings described above, as well as under Vestinautilus 

 jpinguis. 



In addition to these striae there are transverse ones which are to be regarded 

 as lines of growth, as they follow the contour of tlie whorls, and form upon the 

 peripheral area the deep, backward bend which indicates the presence of the 

 hyponomic sinus at the aperture. These lines are sometimes, though extremely 

 fine, remarkably regular, so as almost to raise them to the rank of ornamentation ; 

 they become very crowded close to the aperture ; before this point is attained 

 about eight may be counted in the space occupied by 6 mm. 



Affinities. — The general resemblance of this shell to V. carinifenis is sufl&ciently 

 obvious and has already been dwelt upon ; it differs from it chiefly in the presence 

 of the inner keel of the umbilicus, in its wider septation, in having three more or 

 less distinct keels on the peripheral area, and, perhaps may be added, the fine 

 longitudinal striation recently observed, a feature, however, which V- cariniferus 

 may yet be discovered to possess. 



Bemarlcs. — This is a very common species both in the Dublin district, with 

 which I am best acquainted, and, apparently, in other parts of Ireland. De 

 Koninck refers to it (under the name of Nautilus cariniferus) as being tolerably 

 abundant at Pauquys, Drehance, and Anseremme, in Belgium. 



Localities. — St. Doulagh's, county of Dublin (common) ; Clane, county of 



