TKMNOCHEILUS CORONATUS. 49 



Famihj Tainoceratidj^. 



Genus Tk.mnocheilus, M'Coi/, 1844. 



Tkmnochkii.us cciiiONATus, F. M'Coy. Plate XVIII, figs. 1 a, h, 2 a, b. 



1844. Nautilus (Tkmkocheilus) coeona'ius, F. M'Coi/. '6)-iwy. C-.wh. Fo>s. 



Ireland, p. 20, pi. iv, fi{;. 15. 

 1860. Tksi>ocukilus cohonatus, li. GriJJith. Journ. Geo). .Soc. Dublin, vol. ix, 



!>. 56. 

 1878. Nautilus cono>ATUS, L. G. de Koninck. Faune C'alc. Carb. Belgiquc 

 (Ann. Mus. Eov. d'llist. Nat. Belgique, Pala;ont., 

 toni. ii), pt. 1, p. 115, pi. xxiv, fig. 2. 

 1891. Temnocueilus cobonatus, A. H. Foord and O. C. Crick. Geol. Mag., 



dec. 4, vol. i, ]). 295 (woodciu). 



Description. — SLell tLick-discoid, subglol>ose, the inner whorls exposed in a 

 wide and deep, crateriform umbilical cavity. Tlie whorls are about three in 

 number, with a central vacuity of moderate size and elliptical shape. The section 

 is trapezoidal in form, the ventral area being much wider than the dorsal, which 

 it overhangs considerably. The ratio of the vertical to tho transverse diameter 

 of the whorls may be reckoned at about 22 : 47. The periphery is gently 

 rounded, the margins being marked by the characteristic tubercles. The umbilical 

 walls are very steep, their sides slightly inflated in the lower half. The enrolment 

 completely covers the ventral area up to the row of tubei-cles, wliich are tlius 

 visible on the inner whorls from their first development. 



The septa (not well seen in any of the specimens that have come before me) 

 are about 10 mm. apart on the ventral area, where the diameter of the shell is 90 

 mm. ; they are, therefore, very numerous. The siphuncle appears to be a little 

 above the centre, judging by its position in the type specimen, which is much 

 distorted. 



The ornaments consist of a row of tubercles situated at the angle formed Ijy 

 the junction of the peripheral area with the umbilical wall. Beginning at about 

 the mid-length of the first whorl as obscure undulations, the tubercles gradually 

 increase with the growth of the shell, until at about the second whorl they have 

 become relatively large and prominent. They are of a flattened conoidal form, 

 slightly elongated longitudinally. There are fourteen tubercles to a whorl in an 

 adult shell. A faint raised line encircles the walls of the umljilicus on the innei- 

 whorls just beneath the row of tubercles. The perii)hery is rpiite smooth. 



The young shell is beautifully nuirked with numerous longitudinal tlircad-like 

 lines, which, Ijeiug crossed by the ecjually regular and numerous lines of growth, 



'J 



