FROM THE INFERIOR OOLITE. 267 



Affinities and differences. — The tumid sides, convex upper surface, and marginal vent 

 of Holecti/pus hemisphcBrictis serve to distinguish tliis species from all its congeners, and by 

 these characters it is readily separated from all other Holedypi. 



Locality and Stratiyraphical position. — In the stratigraphical position of this 

 species, I am at issue with the statement made by Professor Forbes, who remarks : 

 " During the examination of the Inferior Oolite strata in Somersetshire and Dorsetshire, 

 by the members of the Geological Survey, this species was collected abundantly, chiefly 

 in the sands of the Inferior Oolite, in numerous places, associated in most instances 

 with Dysaster rinyens, and often Dysaster bicordatus." The following is a list of the 

 principal localities in which it was found : Hazelbury, Crewkerne, Lyttelton Hill, near 

 Cadbury, Whatley, near Frome, Little Windsor, Loders (top beds), Stoke Knaps, 

 Greenland, Compton Pauncefoot (bottom beds), Pilcombe, Bruton, Shipton Gorge, Burton 

 Bradstock, and near Burton Castle (top beds), Bridport Harbour, Chideock Hill, 

 Mapperton, West Swillets, Beaminster."* 



I have never seen this urchin lower than the marly vein which traverses the upper 

 ragstones in the zone of Ammonites Parhinsoni, Sow. ; where I have found it with 

 Cidaris Bouchardii, Wright ; StomecJdnus hiyranularis, Lamarck ; Clypeus Ayassizii, 

 Wright ; Clypeus alius, M'Coy ; Hypoclypus yibherulus, Agassiz ; Ammonites subradiatus. 

 Sow. ; Ammonites ParJcinsoni, Sow. ; Terebratula spharoidalis, Sow. ; Rhynchonella 

 plicatella. Sow. It is true, that in many of the localities in the above list, the ragstones 

 rest on the sands of the Inferior Oolite; a collector, therefore, might readily obtain speci- 

 mens from the sands which had dropped out of the marly seam, and thereby conclude that 

 they belonged to that formation; but I have shownf that the so-called sands of the 

 Inferior Oolite belong to the upper region of the Upper Lias, to the zone of Ammonites 

 Jurensis, Zieten, and Ammonites variabilis, d'Orbig., and that, as far as we at present 

 know, urchins have not been found in this bed. 



I have collected Holectypus hemisphcsricus from the Trigonia grit at Shurdington, Leck- 

 hampton, and Hampen, in Gloucestershire, associated with Pedina roiata, Wright ; 

 Holectypus depressus, Leske ; Echinobrissus clunicularis, Llhwyd ; Echinobrissus Huyii, 

 Agass. ; Clypeus Plottii, Klein ; Ammonites Parkinsoni, Sow. ; and Terebratula glohata. Sow. 



B. Species from the Coral Pay = 14:^ Etaye Corallien, d'Orbigny. 



Holectypus oblongus, Wright, nov. sp. PI. XVIII, fig. 3 a, b, c, d. 



Test oblong, inflated at the sides, depressed at the upper surface ; anterior half of 

 the test shorter, broader, and rounder than the posterior half, which becomes narrow, 



* 'Memoirs of the Geological Survey,' Decade III, pi. 6, pp. 4, 5. 

 t ' Quarterly Journnl of the Geological Society,' vol. xii, p. 292. 



35 



