NOTES AND CORRECTIONS. 



119 



suffered from vertical compression and consequent distortion, so that in many instances it has only been 

 possible, even with the choice of numerous specimens, to select one or two as representatives of their 

 respective species, and some tablets covered with shells have with reluctance been rejected when specific 

 forms could only have been made up by the aid of doubtful restorations. Our note on the age of the 

 gray limestone of the Yorkshire coast alludes to the general identity of species which obtains between the 

 Testacea of the Great Oolite and Forest M&rhle limestones of Gloucestershire and of Oxfordshire; they 

 form, in fact, but one fauna, the most prominent species of which are abundant only over very limited 

 areas. In the Forest Marble claijs we find that the great mass of the organic forms belong to but few 

 genera ; the deficiencies in this respect are very striking. The large collection of Mr. Walton contains not a 

 single Ammonite or Belemnite ; of Gasteropoda there is almost an entire absence of Nerinsea, Cyiindrites, 

 Ceritella, and Trocholoma, genera so abundant and varied in the limestones ; these deficiencies are to a 

 great extent compensated for by an abundance of special forms of Phasianella and of Acteonina, which is 

 the more remarkable as the latter genus is everywhere one of the most rare forms of the limestones. The 

 genus Cerithium is abundant, consisting of forms less dwarfed than is usually seen in the limestones. The 

 genera Nerita, Trochus, and Monodonta, are well represented, but the two latter genera for the most part 

 by forms special to the clays. Of the Conchifera the clays produce Tancredia comparatively in small 

 numbers and apparently of few species, but their condition is usually such as will not admit of a rigid 

 scrutiny ; a similar paucity applies to the Areas, Trigonias, Limas, and Pectens. Perna, Gervillia, 

 Pteroperna, and Astarte, are for the most part represented by species special to the clays or rare in the 

 limestones ; Pholadomya, Homomya, Myacites, and Goniomya, appear to constitute the rarest generic forms 

 in the deposit ; Cercomya and Thracia, perhaps, are absent altogether. Wanting these, tlie clay banks 

 swarmed with a profusion of Nuculae and Cyprinse, usually of forms differing from those of the limestones. 

 Perhaps about 25 per cent, would be a fair estimate of the testaceous species special to the clays ; 

 but taking only the more common forms of each deposit, the differences between them are much more 

 marked and important than would be inferred from such a proportion of species. 



The following, probably, have not been obtained in any other deposit than the Forest Marble : 



Turbo Burtonensis. 

 subtexata. 

 nodifera. 

 Trochus Burtonensis. 

 Monodonta comma. 

 Waltoni. 

 arata. 

 tegulata. 

 Onusbus Burtonensis. 

 Natica arata. 

 texata. 

 alta. 

 Acteonina Luidii. 

 Suessea. 

 fasciata. 

 Wiltonensis. 

 Phasianella variata. 

 Solarium turbiniformis. 

 Waltoni. 



Pleurotomaria Bathonica. 

 Ostrea Wiltonensis. 

 Gervillia Waltoni. 

 Perna obliqua. 

 Trigonia arata. 

 Lucina Burtonensis. 

 Corbis rotunda. 

 Corbula HuUiaua. 

 Islipensis. 

 Agatha. 

 Corbicella subangulata. 

 Cyprina bella. 



Davidsoni. 

 Astarte robusta. 



rustica. 



fimbriata. 



ignota. 



Hilpertonensis. 



Alaria parvula, p. 22. Tab. Ill, fig. 12 ; and A. cirrus, p. 22. Tab. Ill, fig. 13. 



Further observations lead to the conclusion that the former shell is the young condition of the latter, 



