OBSERVATIONS. 13 



name. It is somewhat similar to P. muUicariaatas, Lam., figured and described by the 

 late Dr. Deshayes, ' Descr. de Coq. foss. des Env. de Par.,' p. 307, PL XLII, figs. 17, 

 18, 19, but that is not quite so large a shell, and is said to be from Parnes, in the upper 

 portion of the Paris Eocene. It differs essentially from P. duplicafus, on which the ribs 

 are nearly uniform in size. Our shell is nearly orbicular, covered with ten or twelve 

 large and slightly prominent convex rays, upon which, and also between them are 

 three smaller rays, and between each of these is an alternate smaller one, so that between 

 each of the most prominent there are seven smaller. All of these are ornamented with 

 sharp imbrications, and the shell has unequal auricles, which in our specimen are 

 not quite perfect ; but there are indications of these being of large size in the perfect 

 shell. In the interior of this valve, which is the right one, there are eight or nine 

 furrows corresponding to the elevation of the prominences of the larger ribs. The muscle 

 mark is not very distinct. This specimen, is, in all probability, a derivative from an 

 older formation. 



OBSERVATIONS AS TO THE SUCCESSIVE FORMATION OF THE BEDS 

 FORMING THE APPARENTLY HOMOGENEOUS AND SYNCHRONOUS 

 MASS OF "RED CRAG," AND THE ILLUSORY CHARACTER OF THE 

 EVIDENCE AFFORDED BY PART OF THE ORGANIC REMAINS IN 

 THEM. 



Having in a previous portion of my work on the Crag Mollusca expressed my 

 opinion of the distinctive character of the beds at Walton Naze from the main portion 

 of the Red Crag, and of their older age, I took the opportunity of a few months' stay 

 at Felixstowe in 1879-80 to thoroughly sift and search a large quantity of the Red Crag 

 there, to ascertain not merely what species of Mollusca could be detected in it, but 

 also the general condition in which the remains of these were preserved, so as to compare 

 them with those at the Walton Naze locality, with which, from many visits to that place 

 in the earlier years of my study of the subject, I was very familiar. 



The following list is the result of that investigation ; and in it I have affixed to those 

 species which appear to me to have come into the Red Crag of Eelixstowe only by 

 derivation from beds older than the Red Crag (including those of the Coralline Crag,) 

 the letter D, while to those which appear to me to have come only by derivation froiu 

 earlier beds of Red Crag age, such as that at Walton Naze, I have affixed the letter W, the 

 exclusively fragmentary condition of some species being indicated by the letter F. 



