Dr. A. S. Foorcl — Acanthoiiauiilus, Carboniferous Limestone. 14:9 



Description. — The shell is of medium size, Nautilus-\ikQ in its 

 general habit, somewhat globose, and expanding rapidly. It consists 

 of about two or two and. a half volutions, the inner ones of which 

 are concealed by the lateral expansion of the shell. The peripheral 

 area is broadly rounded and somewhat flattened, on the body-chambei% 

 especially towards the aperture, in the adult, but more narrowly 

 and evenly rounded in the younger stages of growth. The umbilicus is 

 rather large and very distinctly funnel-shaped. It is provided with 

 a thick and very conspicuous rim, which is produced into long, flat, 

 hollow, spine-like processes, projecting almost at right angles to 

 the longitudinal axis of the shell on each side of it. The spines, 

 whose flatness is nearly on the same plane as the surface of the 

 peripheral area, are greatly expanded at their base, but become 

 rapidly narrow towards their distal end, their basal portion merging 

 with a slight concavity in the general surface of the abdominal part 

 of the shell on the outer side, while on the inner side they are 

 continuous with the umbilicus. The spines are met anteriorly by 

 the border of the mouth ; posteriorly by the rim of the umbilicus, 

 from which they proceed on that side. They thus make here a curve 

 on their inner edge which is directed outward and slightly down- 

 ward at the same time. The direction of the spines with reference 

 to the longitudinal axis of the shell is nearly that of a right angle, 

 with a perceptible inclination downwards, that is, towards the 

 septate part of the shell. 



Both the spines are imperfect, one having been broken off near 

 the base, the other at a distance of about 50 mm. therefrom. The 

 former is seen to begin with two diverging folds of the shell, 

 originating as above described. These make an angle, of which 

 the apex is formed by the rim of the umbilicus. The two folds 

 rapidly approach each other, till, as the more perfect spine shows, 

 they run nearly parallel, forming a flattened tube up to the end 

 of the spine, as far as it is preserved. The flattening may be 

 partly due to pressure in the rock, but, on the other hand, the 

 pinched look of the two folds of the shell near the base of the spine, 

 where there is no evidence of crushing, is ah'eady so marked as to 

 contradict the supposition of an artificial flattening of the spine in 

 a great measure. 



The outline of the aperture, which can be accurately traced, is 

 curved gently forward on either side, and forms in the centre a broad 

 and shallow hyponomic sinus. 



The sutures, of which only five are visible, are moderately distant, 

 the last two somewhat closer than the rest. The septa have been 

 completely destroyed by the deposition of crystalline calcite in the 

 chambers, the removal of a great part of which revealed no traces of 

 them ; nor were any remains of the siphuncle found. 



The test is quite smooth, only slightly marked lines of growth 

 occurring on the body-chamber. It is about 1 mm. in thickness. 



The greatest diameter of the shell is 16 cm., measured from the 

 outer margin of the aperture to a point diametricall}' opposite to this. 

 The transverse diameter, measured across the shell Irom the base 



