350 THE LIAS AMMONITES. 



from that species. When it attains twenty millimetres in diameter it assmiies its own 

 typical distinctive shell characters. 



Locality and Stratif/raphical Position. — My figured specimen was collected in the 

 zone of Aey. armatum, near Charmouth ; the same form is found at Robin Hood's Bay 

 in beds of the same age ; the two varieties mentioned by Quenstedt are likewise found 

 there, and have been catalogued by Simpson as {a) cornutus = costatus, Quenst. ; and {b) 

 quadricornutus = nodosus, Quenst. These two forms certainly belong to one species. 



The type specimen which Sowerby figured was found by Mr. Taylor, of Norwich, in 

 a water-worn mass of indurated clay approaching ironstone and containing blende in 

 Happisbury ChfiF, Norfolk, where it was probably alluvial ; it has likewise been found in 

 the Middle Lias of Northamptonshire. A solitary specimen is catalogued by Professor 

 Buckman, F.G.S., from Brickfields, Colthara-field, Hewletts Road, and Leckhampton, 

 near Cheltenham, Gloucestershire. I have never seen a specimen from these beds. 



In Germany, Professor Quenstedt collected it in the Middle Lias at Ofterdingen, 

 Reutlingen, Jebenhausen near Goppingen ; and Professor Oppel in the same horizon near 

 Boll, Metzingen, and Hechingen, where it was common ; in France it was collected by M. 

 Engelhardt at Muhlhausen, Bas-Rhin, in a ferruginous matrix. 



Aegoceras densinodum, Quenstedt. PI. XXXVIII, figs. 5, 6; PI. XXXIX, 



figs. 6— 10. PL L, fig. 11, 12. 



Ammonites armatus densinodus, Quenstedt. Cephalopoden, tab. iv, fig. 18, p. 82, 



1849. 

 — — — Oppel. Mittl. Lias Schwabens, Jahresb. Wurtt., 



p. 71, 1853. 

 Aegoceras densinodum, Neumayr. Zeitschrift der Deutscb. geol. Gesell- 



schaft, p. 906, Jabr 18/5. 



Diagnosis. — Shell much depressed and flattened, whorls very slightly involute; 

 umbilicus wide, with inner whorls all exposed ; spire formed of from six to eight volutions 

 outer whorl with twenty-four to thirty slender, oblique ribs directed backw^ards ; each rib 

 supports one small tubercle near its middle, and a large prominent knob at its termination 

 near the margin ; siphonal area very narrow and depressed, and ornamented with trans- 

 verse strise ; body-chamber long, mouth enlarged with an oblong, trumpet-shaped aperture. 

 Dimensions — Lar(^e specimen. — Plate XXXVIII, figs. 5 and 6 : transverse diameter 110 

 millimetres ; diameter of umbilicus 60 millimetres ; height of trumpet-shaped aperture, 

 40 millimetres ; transverse width 27 millimetres. 



Small specimen. — Plate XXXIX, figs. 6 and 7 : transverse diameter 73 millimetres ; 

 diameter of umbilicus 40 millimetres ; height of aperture 20 millimetres ; transverse 

 width 17 millimetres. 



