204 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



umbilicus. Body-chamber occupying at least half of a whorl. Chambers rather 

 shallow, fourteen or fifteen in a whorl. . . . Test thin, nearly smooth, with obscure 

 lines of growth, which form a shallow sinus on the lateral area, and a broad, shallow 

 sinus on the periphery." (' Cat. Foss. Ceph.,' loc. cit.) 



Affinities. — On comparing this species with Prolecanites ceratitoides, von Buch, it 

 is found to have more rapidly increasing whorls, and it also differs from the latter 

 in its suture-line, in which the peripheral lobe is infundibuliform instead of being 

 expanded posteriorly as it is in von Buch's species. The present species is 

 distinguished from P. similis, Crick, 1 (1) by its more rapidly increasing whorls, (2) 

 by the presence of the conspicuous angular lobe on the inner area of the whorl. 



Remarks. — Although a full account of the history of this species was given by 

 Mr. Gr. C. Crick and myself in the ' Geological Magazine ' for January, 1894 (see 

 synonymy above), it will be useful to recapitulate at least the substance of it, which 

 is as follows: — J. Sowerby described in the 'Mineral Conchology ' (vol. i, 1813) a 

 cephalopod which he named Ellipsolites compressus without expressing any definite 

 opinion at the time as to its affinities. Most succeeding writers have classed it from 

 its general form either with Nautilus or with Discites. In looking over Mr. 

 Wright's collection of fossils at Belfast, I was struck by the marked external 

 resemblance of certain specimens to Sowerby's EIHpsolites compressus, one of them 

 showing very clearly the suture-line characteristic of Prolecanites. On comparing 

 this with Sowerby's two type specimens in the British Museum, it was found that 

 the smaller one of the latter showed unmistakable traces of the same sutural 

 characters, thus establishing the connection between these and Mr. Wright's 

 specimens, while indicating at the same time their generic position. The character 

 of the septa in these forms naturally suggested a further comparison with such 

 species as were known to possess a similar septation; among these the "Ammonites 

 Henslowi " of J. Sowerby was carefully examined, and proved to be identical with 

 " EIHpsolites compressus ; " thus both these names became synonyms of Prolecanites 

 compressus, the specific name " compressus " being adopted in virtue of its priority 

 over " Hensloivi" which was employed by Sowerby seven years later. It is 

 interesting to note that the specimens to which J. Sowerby gave the name 

 Ammonites Henslowi came from the well-known Carboniferous deposits at Scarlet in 

 the Isle of Man, where casts of the species appear to be tolerably abundant. As it 

 has been recognised also from the Carboniferous Limestone of Asturias in Spain, 2 its 

 geographical range is fairly extensive. 



The specimen numbered " G " on P1..XLVII claims attention on account of its 

 being almost completely undistorted. This I consider to be the individual specimen 



1 ' Trans. Manchester Geol. Soc.,' vol. xxiii, 1895, pt. 3, p. 80 ; woodcut, p. 87. Also ' Cat. Foss. 

 Ceph. British Museum,' part 3, 1897, p. 259, fig. 124 (suture-line). 



2 ' Cat. Foss. Ceph. Brit. Mus.,' 1897, pt. 3, p. 254. 



