Vol. 59.] TWO TOARCIAN AMMONITES, 459 



37. Two Toakctan Ammonites. 

 By S. S. Buckman, Esq., F.G.S. (Read May 27th, 1903.) 



[Plates XXVII & XXVIII.] 



Two ammonites belonging to the family Hildoceratidae have been 

 found by members of the Cotteswold Naturalists' Field-Club, and 

 have been given to me to name. Both happen to be new forms ; 

 and they are of particular interest — one for the geological informa- 

 tion which it gives, the other from a biological point of view. 

 The allies of both these species have been figured in my Monograph 

 on the Inferior-Oolite Ammonites (Pal. Soc.) — particularly in the 

 Supplement thereto ; but as I have passed the place where they 

 should have been included, I deem it desirable to lay them before 

 the Geological Society. That they are both new species, and that 

 one of them is particularly distinct, shows that in spite of the 

 number of species described, neAv forms still crop up, and much 

 work yet remains to be accomplished. 



Denckmannia bredojvensis, sp. nov. (PL XXVII, figs. 1-4 h.) 



Description. — Platy - subleptogyral l ; subangustumbilicate ; 

 whorls bullate (on inner margin), rursi-subflexicostate ; septicari- 

 nate, parvicarinate ; periphery subtabulate ; subdensiseptate, with 

 superior lateral lobe broad and subtrilobulate. 



E em arks.— Degenerative changes are marked after about 50 mm. 

 diameter. After that the ornament declines, till in another half- 

 whorl costae and bullae are nearly lost, expansion of the umbilicus 

 begins, and the subtabulate periphery declines to convexi-fastigate. 



Affinity and Distinction. — This species is nearest to Denck- 

 mannia torquata, S. Buckm., 2 but the degenerative changes begin 

 at an early age, consequently it soon shows marked decline of 

 ornament, of which that species gives little indication. 



The small carina distinguishes it from species of Haugia. 



History of Figured Specimen. — Found by Surgeon-Major 

 Isaac Newton in a gravel-pit at Overbury (Worcestershire) on the 

 south side of Bredon Hill, when the Cotteswold Naturalists' Field- 

 Club visited that locality. The materials of this gravel-pit are 

 portions of Marlstone, Upper Lias, and Inferior Oolite, derived from 

 Bredon Hill : consequently there is a mixture of species of the 

 Pliensbachian, Toarcian, and Aalenian Stages. 



Date of Existence. — Probably hemera variabilis, Harpo- 

 ceratan Age (Toarcian Stage). 



Chartrokia costigera, sp. nov. (PI. XXVIII, figs. 1-4.) 



Description. — Subplatyleptogyral, sublatumbilicate : rursi- 

 rectiradiate, costate to pauci- and obscuri-costate ; carinate (? septi- 

 carinate) ; subornatilobate, densiseptate. 



Ptemarks. — The specimen has a practically-complete body- 

 chamber, although the actual mouth-border is not preserved. The 



1 See Note on Technical Terms, p. 4G1. 



2 ' Monogr. Inf. Ool. Amm.' pt. x, Suppl. i, pi. iii, figs. 4-6. (Pal. Soc 



vol. Iii, 1898.) 



