252 ^EGOCERAS, ABIKTITKS, 



phites, Hoplites, Acanthoceras, Stoliczkaia, Crioceras, Heteroceras, 

 Pelfoceras, Aspidoceras. 



Genus JEGOCERAS, Waagen. 



Shell mostly compressed, composed of many whorls, embra- 

 cing but little, sometimes provided with nodose or externally 

 bifurcate ribs; never with true sickle-like ribs; not carinate; 

 body-chamber usually a whorl long, in the geologically younger 

 forms somewhat shorter. Aperture simple without lateral ap- 

 pendages, with very weak external lobes and a constriction; a 

 single corneous apt ychus. Lobular line strongly notched, upper 

 lateral longer than the siphonal, lower lateral not always present; 

 usually with a depending siphoiial lobe. Lobular bodies narrow, 

 not wedge-shaped; antisiphonal two-pointed. 



Several series of forms may be denned, upon the proper refer- 

 ence of which further investigations remain to be made; one of 

 these is that of JEg. incultum, Bey r., to which JEg. palmai, Mojs., 

 Buonarottii, Mojs., planorbis, Sow., Johnstoni, Sow., planor- 

 boides, Sow., etc., are related ; a second series belongs to JEg. 

 subangttiare, Oppel., angulatum, Schl., Gharmassei, Orb.. m<ir- 

 moreum, Op})., and allies; a third is formed by the typical 

 Capricorn* and A rn i a ta, from which Stephanoceras with jEgoceras 

 or Stephanoceras pettos and Davoei have developed; a fourth. 

 ii'oinir back to tlie preceding series is represented by the Falcoida 

 which stand on the border towards Harpoceras. jEg. taylori, 

 Henlciji, alternum, Opp., are somewhat aberrant forms, the inner 

 wliorls of which indicate their allinity to JEgocera*. 



'Pile ti'iie ^Ki/nrrrdft died out in the middle Lias. 



Knur Cretaceous, fifty-lour Liassic species. 



^EGOCERAS BIFERUM, (^uenst. T. 107, figs. 609, <;i<). 



Genus AEIETITES, Waagen. 



Shell Hat. dix-oidal. with wide umbilicus ; on the Hanks simple 

 straiirlit ribs, tlmse on the external angle often angular or in 

 curves directed forwards, frequent ly spinosc. Kxterual si<le 

 carinate, often with two furrows at the sides of the keel. 

 Margin of aperture simple, straight at the Hanks, produced into 

 a pretty long, pointed lobe, which is never bent inwards; body- 

 cliamber embracing one to one and a-<|iiarter whorls. 



