﻿98 MR. S. S. BUCKMAN ON CERTAIN JURASSIC [Feb. I9IO, 



in Burtonia looks as if that part hung from a line which had fallen 

 down at one end. Thus a line connecting the tops of the saddles 

 in JShirbuirnia runs from the periphery n earl y straight to the centre, 

 while the lobes are almost at right angles to it and parallel to one 

 another. But a similar line in Burtonia runs in an oblique curve ; 

 and, instead of the axes of the inner lobes being parallel with that 

 of the superior lateral, they would, if produced, cut. across the axis 

 of this lobe and strike the periphery (see figs. 1 & 2, p. 97). 



This retracted character of suture-line is found in the genera 

 Hammatoceras and Ery cites, to which Burtonia is most nearly allied.. 

 The first is a carinate genus like Burtonia ; the second is not 

 carinate. The character is found in the large uncarinate families 

 Deroeeratidae and Stepheoceratidae ; and it may be concluded that 

 the Hammatoceras series is akin to them, — is probably an offshoot 

 of the Deroeeratidae. The character is not observed in the great 

 carinate groups, the Sonnininae and the Hildoceratidae. In general 

 appearance Burtonia is very like examples of these groups ; and its 

 possession of a carina makes the resemblance closer; but the lobe- 

 character is the distinction. 



Species of this genus characterize the strata of the scissi hemera. 

 Most of the specimens have been found in the beds of this date at 

 Burton Bradstock ; and they may be readily recognized when seen 

 protruding from the massive fallen blocks on the shore. 



Burtonia crassornata, sp. nov. (PI. IX, fig. 1 & PI. X, fig. 1.) 



Description. — Gradumbilicate ; crassornate — inner marginal 

 bullae and coarse costae ; periphery concavifastigate, parvicarinate. 



Bern arks. — The inner whorls, as seen in the umbilicus, show a 

 succession of very strong, closely-set tubercles (bullae) ; on the outer 

 whorl these have declined to coarse, not prominent primary costae, 

 whence proceed the coarse secondary costae. All the ornament 

 gradually declines, and there is a tendency to levigation. 



Distinction. — The species nearest to this — of those yet figured — 

 is Hammatoceras feuguerollense, Brasil 1 ; but the species now de- 

 scribed has a larger umbilicus, coarser ornament, and much stouter 

 whorls. 



Another species, with somewhat generally similar appearance, is 

 Ammonites alleoni, Dumortier 2 ; but his species is flexicostate, and 

 its ornament is much less stout. 



Locality and stratum. — Dorset, Burton Bradstock (Aalenian). 

 [In the bed containing Liocerata and Tmetoceras scissum.~] The 

 figured specimen has no record of its bed : it belonged to my 

 fathers collection, and was probably purchased ; but matrix and 

 condition are good guides. 



1 'Niveau a Ammonites opcdinus' Bull. Soc. Geol. Normandie, vol. xv 

 (1893-94) p. 39 & pi. v, figs. 1-2. 



2 ' Efc. pal. Dep. jurass. Eassin du Ehone ' pt. iv (1874) p. 259 & pi. lii, 

 figs. 3 & 4. 



