Bibliographical Notices. 63 
and Ascoceras. Thirdly we have the “Spirales,” of simple form, 
but with great curvature, and the whorls generally in contact, ex- 
cept Gyroceras, containing Nautilus, Trocholites, Clymenia, &e. The 
members of the fourth group, haying less symmetry and a more 
variable curvature, are associated together as the “ Irregulares,” 
including Trochoceras, Lituites, Ophidioceras. 
Suborder NAUTILILOIDEA (having a variable siphuncle). 
( Orthoceras. 
Endoceras. 
| 
Shellstraight,2 Actimoceras. 
Group I. Contci—Curvature slight or | Tretoceras. 
none; form conical and regu-< Gontoceras. 
TBI ty colle gen sete ene ee te aa | | Conoceras. 
Cyrtoceras. 
Piloceras. 
Trigonoceras. 
Shell curved. 
Poterioceras. 
Group II. Znflati—Curvature slight or none ; form in- ) Gomphoceras. 
rmlani@rel, @aGl TheReraeNe | CG oo nooo cuehoens Phragmoceras. 
Ascoceras. 
( Trocholites. 
; | Clymenia. 
Group IIL. Sperales.—Curvature considerable,form simple.~ Nautilus. 
| Nothoceras. 
| Gyroceras. 
Trochoceras. 
Group IV. Irregulares—Curvature considerable, but vari- | Lituites. 
able ; form irregular or unsymmetrical .. ) Ophidioceras. 
Cryptoceras. 
The genera belonging to the above groups are successively 
noticed, with their synonyms, history, description, and subdivisions 
as adopted by other authors or as followed in this work, and, lastly, 
their range in time and geographical distribution (pp. 48-68), In 
the same systematic manner are the species of the 17 genera and 
subgenera described and carefully figured, so that the student of 
the Palaeozoic Cephalopoda may readily determine any one of the 
143 species (of which 55 are new or renamed) recorded in this 
work (pp. 79-232). Throughout the descriptions the author has 
adopted a somewhat novel but excellent plan in describing actually 
not a species but a single type specimen (except in those referred 
to Bohemian forms), round which the other specimens designated by 
the same name are grouped as closely as they can be. 
Following the type is a general description of other specimens 
referred to the same species, and its relation to other known British 
or foreign forms, and a notice of its geological and geographical 
distribution. 
Commencing with the Conic1, the species of Orthoceras, about 
70 in number, are arranged under two groups, of which 3 belong 
to the Brevicones and the remainder to the Longicones; the latter 
are again divided, according to external ornamentation, into Annu- 
