ARIETITES STELLARIS. 297 



trace in the siplioiial area. The lobe-hne hkewise diflFers from that species, being in 

 general more simple throughout. 



It resembles A. bisulcafus, Brug. (Plates III and IV), in its form, ribs, and keel, 

 but is readily distinguished from it at all ages by the size of the whorls, the more 

 compressed sides, the bevelling away at the outer margin, the complete absence of 

 tubercles on the sides, and the difference in the contour of the lobe-line. 



In youth the ribs in A. stellaris are more acute, in the adult they become blunted, 

 in old age are nearly effaced and the prominent carina becomes much attenuated. 



It very much resembles A. Turneri (Plate XII), but differs from that form in having 

 fewer ribs, all of which disappear on the bevelled margin ; whilst in A. Turneri they are 

 bold and well-defined throughout. The longitudinal and transverse elevated lines, on 

 the shell surface, finely punctated at their intersections, are absent in A. Turneri. The 

 same structural differences distinguish A. stellaris from A. BrooJd (Plate VI), with 

 which it has many affinities in point of form and style of growth. The shell surface, 

 however, forms an important diagnostic character between two such closely allied 

 congeneric forms. 



This is a very important species, and highly characteristic of a well-marked zone of 

 life in the Lias Sea. Prof. Quenstedt described this form as A. Turneri, and assigned its 

 true position in his ' Flozgebirge Wiirtembergs,' p. 156, from its abundance in a bed of 

 clay of his " Betakalk," called " Turnerithone," which he found at Erms by Betzingen, 

 near Balingen, and BoUerbach between Heiningen and Betzgenrieth. 



Dumortier says that it is the most important and characteristic shell of the strata 

 in which it is found, and is the most widely distributed, and is assuredly the fossil the 

 most easy to observe ; seeing that its fragments cannot escape observation, inasmuch as 

 the specimens are almost always of large size. 



Locality and Stratigrajphical Position. — The finest specimens of this species are 

 found in the limestone nodules of the Arietites-ohtusus zone between Broad Ledge and 

 Cornstone Ledge, near Charmouth, Dorset. I have found some large specimens in the 

 same zone in the Bredon cutting of the Midland Railway, and at Robin Hood's Bay, 

 Yorkshire (see page 54). Many of these specimens are preserved in the Leckenby 

 Collection, now in the Woodwardian Museum, Cambridge. 



Foreign Distribution. — South Germany, Wiirtemberg, at Ballingen (Quenstedt) ; 

 Austria, in the North and South Alps (Von Hauer). France: Avallon, Yonne; 

 St. Fortanat, St. Cyr, Dardilly, Rhone (Dumortier) ; Mont-de-Lans, Isere (Gras) ; Nancy, 

 Meurthe, and other localities, together with those recorded in the works cited in the 

 bibliography of this species. 



39 



