230 CCELOCERAS, DACTYLIOCERAS, PHYMATOCERAS. 



Family DACTYLOID^. This taniily includes the Planulati 

 and part of the Macrocephali. 



C(ELOCERAS. Pilje on the abdomen bifurcated ; lateral pilae 

 single or bifurcated with one external row of tubercles, occur, 

 ring regularly on each pilse, or at intervals on widely' separated 

 })ilge. The young are very much flatter than the adults, and the 

 sides consequently very narrow. They are smooth for the first 

 one or two whorls, subsequently becoming tuberculated. The 

 tubercles almost immediately spread, forming the pilte ; they 

 may enlarge and remain distinct, or become absorbed and dis- 

 appt?ar upon alternate pilae. The abdomen remains perfectly 

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

 acquiring the abdominal pilae 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 size, 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. 619, 620. 



Dactylioceras. The 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 

 pilae in the adult are smooth and invariably single ; the abdom- 

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

 the same development as the young of Goeloceras crassum, 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. 



I), annulatus, Sowb. T. 102, figs. 540, 541. 



Family PHYMATOID.E. (Includes part of the Falciferi.) 



Phymatoceras. Abdomen may be flattened or rounded, but 

 never acute ; has no channels in the adult. Envelopment covers 

 the abdomen of each internal whorl. Radii of the spiral increase 

 more slowly than in the succeeding genera. The young are 



