62 Bibliographical Notices. 
and private collections, and thus examine about 2000 well-charac- 
terized specimens during the progress of the work. The first part, 
now issued, consisting of 248 quarto pages of text and 31 plates, 
treats only of the Silurian species. 
Commencing with the general position of the Cephalopoda in the 
animal kingdom, Prof. Blake treats of the chief points in which, as 
a class, they differ from the rest of the Glossophora, as the rudi- 
mentary condition of the foot, the partial segmentation of the ovum, 
and the inflexion of the intestine towards the ventral side of the 
body, in which latter character they agree with the Pteropoda. 
Although the two orders into which the Cephalopoda are divided, 
the Dibranchiata and Tetrabranchiata, are numerically very unequal 
in a living state, yet when the fossil forms are included the pro- 
portion is reversed, the greater number of the latter belonging to 
the second order. 
As the whole of the Silurian Cephalopods, and nearly all the rest 
of the Paleozoic ones, are considered to be tetrabranchiate, their de- 
scription is prefaced by a detailed account of the anatomy of the Naw- 
tilus (pp. 5-17), followed by a description (under nine heads) of the 
structure of the shell and the organs immediately related to it, as 
essentially connected with the better interpretation of the fossil forms 
(pp. 17-41). Of these, the septa and siphuncle are fully considered. 
The size and position of the siphuncle are very variable, and con- 
stitute important characters in the definition of many of the Paleo- 
zoic types, it being either simple or complex, and either ventral, 
median, or dorsal in position. Although there are families with 
non-central siphuncles, still that position is the preponderant one ; 
for Barrande remarks that out of 1500 known forms 500 have central 
and 418 subcentral siphuncles. 
With regard to the classification of the Cephalopoda, after dis- 
cussing the views of other authors, and the position of Bellerophon 
and Clymenia, with which latter genus and Goniatites Barrande 
formed a third group, Prof. Blake divides the Tetrabranchiata into 
two suborders, Ammonitoidea and Nautiloidea. 
As the former suborder is doubtfully represented in the British 
Silurian rocks, he proceeds to discuss the grouping of the genera of 
the Nautiloids, which, according to him, has not hitherto been 
satisfactorily accomplished. ‘‘ The object is not to make a mere 
analytical table, without reference to the history of the group, but 
to show the connexion between the relations in structure and the 
relations in time.” 
The earliest and most important group is that of the Orthocerata of 
extreme simplicity :—(1) with a straight shell, Including Orthoceras, 
Gonioceras, Tretoceras, Endoceras, Actinoceras, Bathmoceras, Bac- 
trites ; (2) with a curved shell, Cyrtoceras and the subgenera Trigo- 
noceras and Piloceras. These form a natural group, and are charac- 
terized as the ‘“‘Conici.” The second group, more restricted in 
time, with slight or no curvature, more or less inflated or irregular 
in form, and with variously shaped apertures, is constituted by the 
“ Tnflati,” and contains Phragmoceras, Gomphoceras, Poterioceras, 
