-loO r<KI,OCKKAS. I. ACTYUOCKKAS. I'll V \l AT< '< ' Kll A S. 



Family DACTYLOID.E. This family includes the Planulati 

 :iml part of the Macrocephali. 



CCELOCERAS. Pil;i- on tile ;il >domen bifurcat ed ; lateral pil;e 

 >ingle or bifurcated with one external row of tubercles, occur, 

 ring regularly on each j)ihi'. or at intervals on widely separated 

 pihe. The young :re very much flatter than the adults, and the 

 sides consequently very narrow. They are smooth tor the first 

 one or two whorls, subsequent ly becoming tnberculated. The 

 tubercles almost immediately spread, forming the pihe ; they 

 may enlarge and remain dist inct . or become absorbed and dis- 

 appear upon alternate pihe. The abdomen remains perfectly 

 smooth for some time after the lateral pihe are developed, not 

 acquiring the abdominal pihe until the third whorl is reached. 

 Septa close together and very intricate in the adult. Abdominal 

 lobe broader and deeper than the superior lateral. The inferior 

 lateral is nearly the same in si/e. and both are unequally divided 

 into three shallow, minor lobes. Superior lateral cell lobiform 

 and together with the inferior lateral, unequally divided by two 

 minor lobes. 



Middle and Upper Lias. 



C. CENTAURUS, d'Orb. T. 107. figs. (',19. fiio. 



HACTYLIOCERAS. Tin- abdomen is either equal in breadth, or 

 less than the back, instead of being broader than, or equal in 



breadth to. the back, as in the preceding genera. The lateral 

 pihe iu the adult are smooth and in variably single : the abdom- 

 inal pihe may be either bifurcated or single. The young have 

 the same development as the young of Coeloceras crastmm, but 

 the tubercles are dispensed with before the adult state is at- 

 tained. Septa do not differ materially from those of the prece- 

 ding genus, except perhaps in the greater simplicity of the lobes 

 and cells, which are hardly so close together or so complicated. 



Upper Lias. 



D. ANNULATUS, Sowb. T. 1 OL>. figs. f>40, 541. 



Family ]'I I V M A T< ) I I ) .K. (Includes part of the Falciferi.) 



PHYMATOOIEAS. Abdomen may be llattened or rounded, but 

 n ver acute : has no channels in the adult. Envelopment covers 

 the abdomen of eacb internal whorl. Hadii of the spiral increase 

 more slowly than in the succeeding genera. The young are 



