1883.] 295 [Hyatt. 



zone in the adults of most species. The young in the adolescent 

 stages have a hollow abdomen with keels, or longitudinal ridges 

 on the abdomen, and forms as in the Triboloceras, but the full 

 grown shells usually become convex on the abdomen with fewer 

 ridges, and in old age are rounded and smooth. Vest, multicari- 

 natus, DeKon. Calc. Carb. pi. 30, remains until late in the adoles- 

 cent stage similar to the adult of Trib. Meyerianum. The genus 

 also contains more involute species. In these the carinations tend 

 to disappear, and the whorls become rounded as in Vestin. glo- 

 batus and Coyanus, DeKon. Calc. Carb. pi. 31. The development 

 is much concentrated in the last, the ridges being suppressed at 

 an early stage. Vest. (N~aut,) Koninckii, DeKon. ibid, p. 139, pi. 

 30, is cited as the type of Ryckholt's genus. 



Koninckioceras, 1 nobis, includes nautilian Carboniferous spe- 

 cies with whorls, having a depressed but broad convex abdomen, 

 trapezoidal in section in the adolescent stages, and similar in 

 form to some species of Triboloceras until a late stage of growth. 

 Sutures have slight lobes on the venter or straight, and broad 

 dorsal lobes, but no annular lobes. Tiiere is an impressed zone 

 on the dorsum, but the umbilical perforation is very large. Type, 

 Kon. (Naut.) ingens sp. De Kon. Calc. Carbon, pi. 23, Mus. Comp. 

 Zool. Camb. Kon. (Naut.) implicatum, ibid, pi. 13, shows the ado- 

 lescent stages. The form of whorl and dorsal lobe appears to 

 place the species in the same series with Triboloceras. 



Aipoceratidae, 



This family is remarkable for the rotund form of the adoles- 

 cent and adult whorls, and most species have a trumpet-like or 

 flaring aperture. The peculiar heavy ridge of the umbilical 

 shoulders in the nautilian forms is also a marked peculiarity. 

 The siphon is in most forms close to the venter, but in some be- 

 tween the centre and the venter. The Sactoceran peculiarities 

 of the radical species separate the group from any series to which 

 it might have been otherwise referred. 



Aploceras D'Orb. Prod. Pal. Vol. 1, p. 112, includes a series 

 of arcuate Carboniferous forms described by DeKoninck, Calc. 

 Carb. These have a brevicone aspect in most species, the shell 



1 Dedicated to Prof. L. DeKoninck. 



