120 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



Dimeiisions. 



Specimen in Museum of 

 Science and Art, Dublin.' 



Diameter of shell . . . .160 mm. 



,, umbilicus . . .2-5 ,, 



Height o£ outer whorl (dorso-ventral) . . 80 ,, 



Thickness at umbilical margin . . . 100 ,, 



Width, of shell (ventrally) just above the origin of 



the spines .... 120 „ 



Width of periphei'y at aperture of shell . . 90 ,, 



Acuities. — I have drawn attention elsewhere " to the resemblance between the 

 present species and the one described under the name of Nautilus cornutus by 

 Golowkinsky,^ from the Permian formation of the central part of the basins of 

 the rivers Kama and Volga. I am now enabled, through the kindness of a friend, 

 to give a translation of the original description fi'om the Russian of that author, 

 by which the two species may be more satisfactorily compared. It runs as 

 follows : — " It \N. cjyrnvtus] has three or four whorls, which grow quickly in 

 breadth, forming a deep umbilicus ; each whorl covers about half of the preceding 

 one, and has, when cut transversely, the form of a crescent with rounded ends. 

 The periphery is flattened in large specimens. The sutures form a slightly waved 

 line, which curves backwards on the umbilical whorl and on the sides of the shell, 

 and more slightly so upon the periphery. Tiie siphuncle lies nearer to the 

 umbilicus than to the periphery, and is therefore a little below the centre of the 

 septa. The body-chamber occupies approximately one-third of the last whorl, 

 and presents at tlie aperture a roimdish contour, with a sharp angle on each side 

 where the lateral margin unites with the umbilical wall. Here, taking a course 

 almost at right angles to the pei'iphery, a tubular process [spinej is formed, which 

 juts out from each side of the aperture like a horn. 



" Thus the horn-like spines are formed by a fold in the test, which unites along 

 a line extending outwards from the lower angle of the apertural margin. The 

 extremity of the spines is open. Their general direction is nearly at right angles 

 to the longitudinal axis of the shell; but they have a strong upward inclination, 

 and are also slightly curved. In the large specimen [figured], measuring 100 mm. 

 in diameter, the length of the spines is 55 mm. The periphery at the apertui*e 

 projects a little in front of the spines. The surface of the shell is covered with 

 fine lines, which, upon the periphery, form a backwardly directed, very small 



' A cast has been deposited in tlie Britit^li ^luseuni. 



* ' Geological Magazine,' New Series, decade 4, vol. iv, p. 287. 



^ ' Materiaux pour la Paleontoloirie Russe,' torn, i, IS69, p. 381, tab. v, figs. 15 — 19. 



