282 



Revieics — Messrs. Foord and Crick — 



These embryological studies of the shell bring out also most 

 clearly the fact that in the earliest stages the great divisions of the 

 Cephalopoda converge towards each other, and we arrive nearer to 

 a common radical for the whole. Hence the difficulty which some 

 authors have felt in deciding whether the genus Bactrites has 

 stronger affinities with Goniatites or with Orthoceras. 



Fig. 2. — Brancoceras Iccion, J. Hall, sp. a, lateral Tiew of a natural cast, from 

 Goniatite Limestone, Kinderhook Group, Kockford, Indiana ; b, peripheral view of 

 same ; c, suture-line ; tl, pei'ipheral lobe ; es, peripheral saddle ; II, lateral lobe ; 

 Is, lateral saddle. -| nat. size. (Fig. 62, p. 132, op. cit.) 



The authors give us a clearly defined, yet comprehensive diagnosis 

 for the suborder Ammonoidea, as follows : — " Shell conical, involute 

 (most forms), or partly involute and partly evolute (Scnphites) ; some- 

 times bent on itself at one or both ends (PtycJioceras, Diptychoceras) , 

 or hook-like {Hamites), or even turreted (Turrilites), etc., or essen- 

 tially straight (Baculites). Aperture simple, or with variously- 

 formed lateral and ventral expansions. Suture-line undulating, 

 serrated, or with more or less numerous digitate branches. 

 Siphuncle marginal, without internal deposits. Initial chamber 

 spherical or ovoid. Aptychus or anaptychus often present." 



After discussing the merits of Dr. Paul Fischer's terms Retro- 

 siphonata and Prosiphonnta, the authors mention that Dr. E. Haug 

 has pointed out that the Ammonites are retrosiphonate in the young, 

 and that sometimes the prosiphonate stage is not attained (as in 

 TiroUtes) until the shell has reached a tolerably advanced age, 

 a little before the last chamber. Instead of these terms, therefore, 

 they rely on the important character of the sutures and divide the 



