170 



argillaceous limestone called White Lias. In the Yorkshire coast it is 

 found in large water worn boulders at Robin Hood's Bay; the best 

 specimens I know have been obtained from these blocks, in which it 

 lies in clusters. The beds from whence these boulders have been detached 

 are out at sea, as the rock is not found in situ at low water mark. 



Ammonites angulatus, Schlotheim. (PI. 1, fig. 4, a, b, fig 5.) 



Ammonites angulatus, Schloth., Petrefactenkunde, p. 70, 1822. 



II Redcarensis, Toung & Bird, Geol. Survey, Yorkshire Coast, 



n anguliferus, Phillips, Geol. of the Yorkshire Coast, p. 192, 



vol. 1, tab. 13, fig 19., 1829. 

 II COLUBRATUS, Zieten, Versteinerungen Wiirtembergs, tab. 3, 



fig. 1, p. 3, 1830. 

 II CATENATUS, d'Orb., Pal. Fran. ter. Jura., tab. 94, p. 301, 1842. 



M MoREANUS, d'Orh., .i n tab. 93, p. 299, 1842. 



I- Charmassei, d'Orb., n m tab. 94, p. 296, 1842. 



II Leigneletxi, d'Orb., m m tab. 92, p. 298, 1842. 



II ANGULATUS, Quenst., Cephalopoden, p. 74, pi. iv., fig. 2, 1846. 



II ANGULATUS, Quenstedt, Petrefactenkunde, p. 354, tab. 27, 



fig. 7, 1852. 

 II ANGULATUS, Quenstedt, der Jura, p. 43, tab. 3, fig. 1, 1858. 



II ANGULATUS, Chapuis et Dewalque, FossUes de Luxembourg, 



p. 36, pi. iv., fig. 1, 1853. 

 II Redcarensis, Simpson, FossUs Yorkshire Lias, p. 100, 1855. 



Diagnosis. — ^Young shell compressed, whorls involute, half enveloped ; 

 sides with numerous, 26 to 30, sharp, simple, flexed ribs, which pass round 

 the dorsal border, and terminate abruptly in a furrow in the centre of 

 the back, or in a smooth truncated surface. 



Adult shell, seven inches in diameter, compressed ; whorls flattened, 

 sloping towards the back; sides smooth, with long, faint, biflexed ribs, 

 and shorter and more marked ribs near the dorsal border ; back narrow, 

 round, smooth ; aperture compressed. 



Dimensions. — One of my largest specimens from Lyme Regis measures 

 seven inches and two-tenths in diameter. Height of the last whorl near 

 the mouth is two inches and six-tenths ; width, one inch and four-tenths. 

 Wliorls one-half covered by the involution of the spire. 



Description. — Like many other Ammonites, this species must be 

 studied at different stages of growth, if we are rightly to understand its 

 true characters. Up to about the diameter of an inch the whorls have 

 from 25 to 30 shai'p simple ribs, which terminate abruptly and form a 

 jnarked angle on the back — hence the origin of the specific name; at a later 



