1865.] Geology and Paleontology. 105 



and more or less completely nacreous, extension forwards of the lip 

 of the phragmocone. 



" 2. According to Agassiz, it is a ' pen ' identical with that of the 

 so called Loligo Bollensis, &c. 



" 3. According to Voltz, it is a ' pen ' analogous to that of Loligo 

 Bollensis. 



" 4. According to Mantell and Quenstedt, it is a broad dorsal plate, 

 more or less corneous in the middle, and with two strong calcified 

 asymptotic bands." 



Professor Huxley's own opinion we have already given, but the 

 most novel portion of his views on the subject, is the belief in the 

 systematic importance of the variations in the form of the pro- 

 ostracum, and on this account he is disposed to favour a subdivision 

 of the genus Belemnites itself, " the difference between the pro-ostraca 

 of B. Bruguierianus and B. Puzosianus being, probably, of generic 

 importance." 



Another new point is the direct proof, furnished by the specimen 

 we have figured, of the existence of beaks and acetabular hooks in 

 the genus Belemnites (see Fig. 1 / and Fig. 2) ; for though they have 

 long been known to exist in Belemnoteuthis, they have never before 

 been found in Belemnites. 



Professor Huxley also describes a new genus of Belemnitidai. In 

 1829 Sir Henry de la Beche figured and described a remarkable 

 specimen from the Lias of Lyme Regis under the name of OrtJiocera 

 elongata, the true nature of which has only recently been made out 

 by the author, from the study of -a very perfect specimen not long 

 since discovered by E. C. H. Day, Esq., F.G.S., of Charmouth. Pro- 

 fessor Huxley describes this and the original Orihocera at length, 

 and, as the newly found specimen shows that the pro-ostracum 

 belonged to a type distinct from either of those occurring in the 

 genus Belemnites, he refers the two specimens to a new genus under 

 the name of Xiphoteuthis elongata ; he gives a full account of its rela- 

 tions to other Belemnitidai so far as can be ascertained from the speci- 

 mens, but states that several points are still unknown or obscure. 



The second part of the Philosophical Transactions for 1864 con- 

 tains the following papers by Mr. Prestwich, the first two having been 

 incorporated together under the double title : — 



1. Theoretical considerations on the conditions under which the 

 (drift) deposits containiifg the remains of extinct mammalia and 

 flint implements were accumulated, and on their Geological age. 



2. On the loess of the valleys of the South of England, and of the 

 Somme and the Seine. 



3. On some further evidence bearing on the excavation of the 

 valley of the Somme by river-action, as exhibited in a section at 

 Deucat, near Abbeville. 



In these papers the author discusses the mode of formation of the 

 beds containing flint implements, and of the river- valleys in which they 

 occur. He first shows that the gravel-beds follow, at various levels, 

 the course of the present valleys, and have a direction of transport 

 coincident with that of the present rivers ; but the fact of some of the 



