502 Notices of Memoirs — S. S. Buckman — Ammonite Zones. 



upon which the 'nipple,' or apical tubercle, is present — must be 

 sought amongst the various species of Colohodus and Lepidotus (of 

 Plieninger, 1847) ; whilst intermediate forms, or those from which 

 the ' nipple ' has been partly or entirely removed by wearing or by 

 post-mortem abrasion, must be sought amongst those described under 

 the various species of Lepidotus, Sphcerodus, Gyrodtis, ' Tetragonolepis ' 

 (of Winkler, and of Agassiz in part), Tholodus and Thelodus, Eupleu- 

 rodus, Sargodon (not cutting teeth), and even amongst teeth variously 

 attributed to Saurichthys and to ' Saurians,' whilst the chisel-shaped, 

 or pre-maxillary, teeth are probably those attributed to Sargodon 

 tomicus. 



Fragments of the head and trunk and scales of Colohodus have 

 been described or figured by H. B. Greinitz, Meyer and Plieninger, 

 Giebel, Meyer, Quenstedt, Eck, Kner, H. Kunisch, W. Dames, J. 

 von Eohon, and A. S. Woodward, and must be sought amongst the 

 various species ascribed to Gyrolepis and Amblypterus, Lepidotus, 

 Heterolepidotus, Eugnaihus, Pleurolepis, Dactylolepis, and also amongst 

 various Ganoid scales (' Ganoidschuppen ' and ' Fischschuppen '). 



Up to the present neither the teeth nor the scales of Colohodus 

 have been recognized as such in Britain by any authors, or, above 

 the Muschelkalk and Lettenkohle, abroad : its occurrence and recog- 

 nition, therefore, in the Ehsetic of Britain is interesting, and the 

 author exhibits typical and transitional teeth which he found and 

 recognized in the Khastic 'bone-beds' of Wachet and Aust Cliff; 

 worn and abraded teeth (' Sargodon tomicus ' and ' Sphoerodus ') from 

 thence and from Leicestershire ; and what are probably the larger 

 cutting teeth from Aust and Leicestershire ; also fine characteristic 

 scales and (? head-)bones showing vermiculated sculpture from 

 Aust. All may, for the present, be referred to Colohodus maximus 

 (Quenstedt), 



Finally, should Colohodus prove to be identical with Lepidotus, a 

 fusion of Heterolepidotus and EugnatJms will give Colohodus a more 

 extended upward range than has hitherto been supposed. 



V. — The Ammonite Zones of Dorset and Somerset. By S. S. 

 BxjCKMAN, F.G.S., Hon. Memb. Yorks Phil. Soc. 



THE lower part of the Murchisonte-zone is often intimately con- 

 nected with the upper part of the Opalinum-zone ; but, a little 

 higher, there is an horizon characterized by numerous specimens of 

 Liid'wigia MurcMsonce. The fauna of this horizon corresponds to the 

 MurcMsonce-zone of Oppel, and to the Brauner Jura /i of Quenstedt. 

 Above the MtircJiisonce-zone a considerable break in the sequence of 

 strata is frequently met with. In the neighbourhood of Bradford 

 Abbas, however, is found, superior to the Murchi&once-zone, an 

 horizon marked by a very peculiar fauna, in which Lioceras concavum 

 and species of the genus Sonninia predominate. Taken in a general 

 sense the fauna of this zone {Concavum-zone) does not agree with 

 that of Quenstedt's Brauner Jura (3 or 7, nor with that of the 

 Sowerhyi-zone, as illustrated by Waagen, Douville, etc. Further,- 



