510 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Opliioderma, joints. 



Pentacrinites. 



Serpula, 



Entomostraca, sp. 



Discina Davidsoni, Moore. 



Terebratula punctata,(strangulata Terq.) 



Khynchonella variabilis* 



Spirifera Walcottii, Sow. 



Avicula decussata. 



Grypb.£ea incurva, Sow. 



Lima gigantea, Sow. 



tuberculata, Terq. 



duplicata. 



' ) sp. 



Ostrea intusstriata, on chert pebble. 

 — ■ — arietis. 



liassica. 



irregularis. 



^pondylus liassicus, Terq. 

 Pecten Pollux, D' Orb. 



Pecten sublcevis. 

 Pinna semistriata, Terq. 

 Plicatula Hettangiensis, Terq. 

 Cardinia Listeri. 



elongata. 



Modiola, casts of. 



producta, Terq. 



Myacites. 



Pholadomya ambigua. 

 Unicardium cardioides. 

 Cerithium nodulosum, Moore. 



paludinare, Terq. 



, sp. 



Turritella Deshayesii, Terq. 

 Littorina clathrata, Desk. 

 Melania (Pterocera) dubia, Terq. 

 Pleuro torn aria densa, Terq. 



Hettangiensis, Terq. 



expansa, Sow. 



Solarium lenticulare, Terq. 



8. Value of Zones of Zoolor/iccd Life. — Before passing to a consi- 

 deration of the Secondary rocks of South Y/ales, it may be desirable 

 to saj^ a few words on the value to be attached to precise zones of 

 zoological life. Although it is exceedingly convenient to the geo- 

 logist to be able to refer certain fauna3 to horizons such as those 

 known as Ammonite -zones, of which, as far as possible, I have 

 availed myself, still, with our increased knowledge of the range of 

 specific forms, such limits may prove arbitrary and may mislead. In 

 the same district, or even at wide intervals, as is the case with the 

 Upper Lias of Ilminster and of May in Normandy, or Whatley ar.d 

 Pontaine-etoupe-Pour, where beds have been deposited under the 

 same physical conditions, we may expect, as a general rule, to 

 find identical species, or even, after a considerable interval in time, 

 when favourable conditions occurred, to find their recurrence ; but 

 when the beds have been otherwise deposited, it would not be sur- 

 prising if this law failed. I have previously shown such recur- 

 rence with some of the Brachiopoda, and it is also the case with 

 many of the Eoraminifera. 



Avicula decussata has hitherto been considered to belong only to 

 the Ehsetic *' White Lias ;" but we now find this species to occur 

 in the Lower Lias of Hatch, Camel, and Bedminster, and in the 

 Ammonites- BucTclandi beds of Shepton. Ostrea intusstriata was 

 also supposed to be confined to the Ehsetic beds ; but it is abundant 

 at Sutton, passes through the Liassic beds of Bridgend (fee, and is 

 found with the Ammonites Biicldandi at Shepton and Bath. Erom 

 the latter quarries I have it attached to the interior of Gryphaa 

 incurva, and also to the exterior of a large Ammonites angulatus from 

 the same beds, to which there are not less than 114 attached 

 specimens. Ostrea liassica is abundant in the ^' White Lias," but 

 has its greatest development in the Ostrea-beds of the Lower Lias, 

 and then passes upwards, though more sparingly, into some of the 

 higher beds. 



The same may be shown of the range of many of the Ammonites. 



