310 



THE LIAS AMMONITES. 



several new forms to the division Psilonoti. The oldest representatives of this section, 

 according to Beyrich, are found in the Muschelkalk of the Alps and of the Himalayas, as 

 Aeg. incultum, Beyr., Aeg. Salteri, Beyr., Aeg. Palmai, Mojs. In the Rhaetic beds 

 of the Bavarian Alps, Dr. Giimbel found Aeg. planorboides, Gurnb. ; and in the 

 Lower Lias the following species are recorded : 



Aegoceras planorbis, Sow. 



— calliphyllum, Neum. 



— Hagenowi, Dunk. 



— torus, d'Orbig. 



— Johnstoni, Sow. 



— tortile, d'Orbig. 



— crebrispirale, Neum. 



— magus, Neum. 



— Clausi, Neum. 



Aegoceras laqueus, Quenst. 



— laqueolus, Schlonb. 



— Gernense, Neum. 



— JSuessi, V. Hauer. 



— Aeduense, d'Orbig. 



— Belc/ieri, Simp. 



— intermedium, Portlock. 



— liassicum, d'Orbig. 



— Naumanni, Neum. 



In the absence of specimens wherewith to compare the minute differences which 

 have been observed in the lobe-line of several of the forms in the preceding list, I must 

 refrain from giving an opinion on the specific distinctions of the same, seeing that it is 

 extremely difficult to arrive at a satisfactory conclusion as to forms which even have 

 generally been admitted to be distinct, nor can a safe conclusion be attained unless we 

 have before us several specimens showing the changes of form they assume at different 

 phases of growth. 



Prof. Quenstedt, in his ' Cephalopoden,' p. 73, admits two varieties, Am. psilonotus 

 lavis, Qu., and Am. psilonotus plicatus, Qu. ; the former with a smooth shell, and the 

 latter with a folded or plicated shell. I have before me good examples of these varieties 

 kindly sent by Prof. Fraas from the Stuttgart Museum, which fully bear out my learned 

 friend's description. 



The affinities and differences existing between Aeg . planorbis and other species of the 

 section Psilonoti are numerous and not easily determined. 



Locality and Stratigrap/iical Position. — I have collected Aeg. planorbis in the lowest 

 beds of the Lower Lias, and whenever they are exposed it forms their most characteristic 

 leading fossil. It is very abundant in the paper-like shales of this zone at Brockeridge 

 and Defford Commons, Gloucestershire, at Burton, Wilmcote, and Grafton, Warwickshire ; 

 at Street, Uphill, and Watchet, Somersetshire ; Penarth, Glamorganshire ; and Pinhay 

 Bay and Uphill, near Lyme Regis, Dorsetshire, where it is found in the upper part of 

 the light-coloured argillaceous limestone, called there White Lias. On the Yorkshire 

 coast it is found in large water-worn boulders of light-coloured limestone washed up by 

 the tidal currents, and in the North Cliff of Robin Hood's Bay ; and in Eston and East 

 Coatham pits. The beds from which the masses are derived are out at sea, as the rock 



