1896.] -^^7 [Smith. 



the same group as G. russiensc. Dr. K. von Zittel, in Griidzilge der Pal- 

 leontologie, 1895, p. :599, confines Gastrioceras to forms with a single pair 

 of lateral lobes. But tlie relations of Gastrioceras, Glyphioceras and 

 Paralegoce.ras have been best worked out by Karpinsky,* who shows 

 that there is no marked distinction between Glyphioceras and Gastrio- 

 ceras ; that both have the same number of lobes and saddles — nine of 

 each ; that the second pair of lateral lobes may be on the umbilical 

 shoulders or on the sides of the shell, thus differing from Paralegoceras, 

 in which the third pair of lateral lobes is on tlie umbilical shoulders. 

 Gastrioceras usually has a trapezoidal cross-section and umbilical ribs; 

 but some species lack the ribs, as G. glohulosum M. and W., Avhile some 

 species of Glyphioceras have umbilical ribs and, in their youth, also the 

 elliptical cross-section, as Glyphioceras cliadema Goldfuss. But the two 

 extremes are widely separated from each other, as Gastrioceras jossce 

 Verneul and Glyphioceras sphcericum Martin. 



This genus has been looked upon by Steinmannf as the ancestor of the 

 trachyostracan families of the Trias, the Ceratiiidm and the Tropitidve. 

 Dr. K. von Zittel % agrees with this opinion as to the origin of the Trop- 

 itido', but thinks the Geratitidm developed out of the Prolecanitidte. 



Gastrioceras hranneri sp. nov. J. P. Smith, PI. xxiii, Figs. 1-6. 



The adult shell is discoidal, with low, narrow wliorls of semilunular 

 cross-section ; the adult whorl is very evolute, embi-acing not more than 

 a third of the preceding one, and the increase in height and breadth is 

 extremely slow. The young whorls are proportionally broader and 

 more involute, so that the umbilicus of the younger part of the shell is 

 deeper, but widens rapidly with age, as the involution decreases. 

 G. branneri is the most evolute species of Gastrioceras known in the 

 Carboniferous, and approaches the narrow evolute Permian type, 

 described by Gemmelarog from Sicily ; but the Sicilian form still retains 

 the strong constrictions, and has also acquired the spiral striaj tliat are 

 characteristic of Permian Gastrioceras. 



Dimensions. mm. 



Diameter 39.5 



Height of last whorl 10.5 



Width of umbilicus 19.0 



Breadth 15.0 



Height of last whorl from top of preceding 8.0 



The specimen shows nine whorls at the diameter of 89.5 mm. 

 Sutures. — The sutures consist of three external lobes and as many 



* Mem. Acad. Impcr. Sei., St. Petersburg, vii Ser., Tome xxxvii, No. 2, " Ammoneen d> 

 Artinsk-Stufe," pp. 45-48. 



t Elemente d. Palxontologie, 1890, p. 393. 



X Grundzilge d. Palxontologie, 189J, p. 405. 



§ Giorn. Sci. Nat. ed. Scan., Vol. xx, 1890, p. 31, PL D, Figs. 21-20, Gastrioceras waageni 

 Gemm. 



PHOC. AMER. ririLos. soc. XXXV. 152. 2g. pkixted dec. 9, 1896. 



