﻿"92 ME. S. S. BUCKMAN ON CERTAIN JURASSIC [Feb. I9IO, 



the suture-line has somewhat this pattern, but is less lobulate, 

 the stout whorls, the coarse ornament, and the smallish carina, are 

 distinctions. 



In Sonninia the whorls are much compressed; the carina is 

 very strong — it is distinctly an alticarinatc genus ; the suture-line 

 is very complex ; the lobes are long ; the superior lateral lobe is 

 narrow- stemmed. In Dorsetensia (D. liostraca series) the whorls 

 are much compressed and the carina is very strong ; but the suture- 

 line is of a type much simpler than in Shirbuirnia. From the 

 ' Sonninioi of the concavum zone ' there is no need to consider the 

 various distinctions, because they ought to be separated from 

 Sonninia. From Dorsetensia edoiiarcliana, which is the type of the 

 genus Dorsetensia, there is also little need to consider distinctions ; 

 the regular costate stage and the absence, except on inner whorls, 

 of a tuberculate stage, show the different line of development in 

 that case. 



Shirbuirnia trigonalis, sp. nov. (PI. X, figs. 2 & 3.) 



Description. — Gradumbilicate ; ornament-stages irregularly 

 tuberculate-costate, declining to levigate. 



11 em arks. — The inner whorls show various small eostre, with 

 occasional irregular, inner marginal nodi. Later these ornaments 

 decline into complete smoothness. 



The trigonal shape of the whorl gives a pronounced wall to the 

 umbilicus. Specimens of this species have lain in my cabinet, 

 with the description now given, for some dozen or more years 

 awaiting description. The species is interesting, because its fellows 

 are found in Wiirtemberg * ; and because the fauna which they 

 typify is only found in perfection in one place in England, namely, 

 at Sandford Lane Quarry, Sherborne (Dorset). 



Locality and stratum. — Dorset, Sherborne, at Sandford Lane 

 Quarry, in the bottom part of the Fossil Bed ; Bajocian. 



Date of existence. — Sonnini<*> hemera. This should now be 

 altered to hemera of Shirbuirnia trigonalis ; for Sonninia sensu 

 stricto belongs only to the sauzei hemera. 



The holotype of this species is a large adult specimen, which 

 could not be adequately figured in these pages. It is about 325 mm. 

 in diameter, showing little else than a smooth catagenetic stage. 

 The umbilicus expands in the last turn, attaining «a breadth of 

 120 mm. The whorl-section becomes more and more trigonal or 

 galeatiform with age, the breadth of the whorl just about the inner 

 margin being about 98 mm., making allowance for the thick test 

 which borders the umbilicus. The umbilical bordering wall becomes 

 very conspicuous. 



The paratype specimen, of which figures are given (side view 

 xO-86 and front view xOGl), shows the nodaticostate stage of 

 the inner whorls (the nodi being somewhat irregular swellings on 

 the inner margin) passing into the levigate stage. 



1 See the Ammonites sowcrhyi fauna figured by Quenstedt, ' Amm. Schwab. 

 Jura ' 1886, pis. lxi & lxii. A. sowerbi/i yraciUlohaius is possibly a Shirbuirnia. 



