ORTHOCERAS PERCONICUM. 27 



the surface of such shells, and apparently no distinction was made between what 

 are properly termed "imbricating" lines and other fine transverse lines of a 

 totally different nature. 



I would suggest, therefore, that the name " Orthoceras cinctum " be given up, 

 since its further employment can only lead to confusion.] 



B. Brevicones. 

 Orthoceras perconicum, A. H. Foord. Plate VIII, figs. 4 a,b. 



1S96. Orthoceras perconicum, A. H. Foord. Ueber die Oithoceren des 



Kohlenkalks (Carboniferous Limestone) von 

 Irlaud. . . . Inaugural-Dissertation zur 

 Erlangung der Doktorwiirde . . . der 

 Kg], bayer. Ludwig-Maximilians-Universitat 

 zu Miiuchen, p. 36. 



Description. — Shell abruptly conical ; rate of tapering very rapid, that is 

 about 1 : 2. The transverse section is slightly elliptical, the proportion of the 

 two diameters being as 35 : 29. The body-chamber is very large, occupying fully 

 half the length of the entire shell, and far exceeding it in bulk. Only the sutures 

 are seen, the septa themselves, as a section proved, having been completely 

 destroyed ; they are perfectly horizontal. The siphuncle is not preserved. The 

 only example obtained measures 86 mm. in length ; the greater diameter amounts 

 to 47 mm., the lesser to 16 mm. (this is considerably above the apex). The test 

 is perfectly smooth. 



Size. — Length (imperfect at both ends) 86 mm. ; greatest diameter 47 mm., 

 least 16 mm. 



Affinities. — In seeking for a species related to the present one, that described 

 by de Koninck from Vise, Belgium, under the name of Orthoceras cucullus l at 

 once presents itself to our notice. This consists only of the chambered part of 

 the shell, so that the proportions of the body-chamber in relation to the complete 

 shell cannot be compared with those of 0. perconicum. The rate of increase in 

 the diameter of the Belgian species is 1 : 2'66; that of the Irish species, as 

 indicated above, 1 : 2. The sutures are rather wider apart in 0. cucullus than they 

 are in 0. perconicum; that is, in an interval of 28 mm., measured off at the 

 smaller end of each specimen, there are five chambers in the latter against four 

 and a half in the former. Both species are unfortunately only imperfectly known. 

 In 0. cucullus the body-chamber and the test are wanting, in 0. perconicum the 

 siphuncle and the septa (not their sutures) have been destroyed. There are thus 



1 ' Descrip. Anira. Foss. Belg.' (Suppl.), 1851, p. 54, pi. lix, fig. 1. 



