TURRILITES. 03 



it was long confounded. M. D'Orbigny pointed out the distinctions between them, which 

 consist in the shorter and blunter spire, fewer and larger tubercles of T. Gravesianus. 

 Slightly crushed specimens of T. tuber culatus are sometimes very difficult to distinguish 

 from T. Gravesianus, unless the outline of the septa can be traced, when the different forms 

 of the dorsal saddles set all doubts on the subject immediately at rest. 



3. Turrilites Mantelli, Sharpe. Plate XXV, figs. 5 and 6. 



T. testa turrita, sinislrorsd : anfractibus numerosis, extra convexis, tuberculatis : tuber- 

 culis 4 serialibus ; serie superiori, in medio anfractuum, tuberculis 20 — 24, basi rotundatis ; 

 seriebus tribus inferioribus, tuberculis 30 minoribus, basi elongatis, approximatis : angulo 

 spirali 18°— 20°. 



Shell turreted, with a spiral angle of 18° to 20°, sinistral: whorls numerous, convex 

 externally, with one row of 20 to 24 tubercles near their middle, and three rows of about 

 30 smaller tubercles near their base, the lowest of which rows is hid by the suture; the 

 tubercles of the middle row have a rounded base, those of the three lower rows are 

 elongated in a direction parallel to the suture, and are of the same number in each row : 

 upper and lower sides of the whorls ornamented with radiating ribs, corresponding to the 

 tubercles of the lower row : umbilicus narrow -. mouth somewhat produced, and rising to a 

 blunt point on the inner side of the whorl, and surrounded by a broad, wing-shaped 

 expansion of somewhat rhomboidal form. 



Only a small part of the outline of a septum has been seen, which is shown on the 

 upper whorl of fig. 5 ; the dorsal saddle is divided into two unequal parts, which are inter- 

 mediate in form between those of T. tuberculatum and T. Gravesianus, more nearly 

 resembling the latter. 



Diameter of last whorl, 2^ inches; probable length, 12 inches. 



Rare in the Grey Chalk, near Lewes, Sussex. 



This species is readily distinguished from T. tuberculatum by the greater number and 

 smaller size of the tubercles of the upper row, which are almost as numerous as those of 

 the three lower rows. There is also a marked difference in the rhomboidal form of the 

 expanded margin of the mouth. These distinctions will probably be strengthened when a 

 more complete view is obtained of the lobes of the septa. 



The only specimens which I have seen were collected by Dr. Mantell, and are now in 

 the British Museum. The specific name is therefore a just tribute to the memory of that 

 zealous geologist. 



