FROM THE CORNBRASH. 343 



The apical disc is large, and presents a very remarkable modification of the usual type 

 of structure observed in other Echinobrissid^. As I have seen this structure in 

 many specimens collected from localities widely apart, it must be regarded as a normal 

 form in this species. Mr. Bone has figured this curious disc with great accuracy at 

 fig. 2 d; the two pair of perforated ovarial plates have a pyriform shape, the right antero- 

 lateral is the largest, and supports the spongy madreporiform body ; between these there 

 are introduced into the middle of the disc four small plates, and posterior to them three 

 other smaller plates. The front rows are bounded before by the madreporiform plate, 

 and behind by the left posterior ocular plates, and the three posterior plates He between 

 the posterior oculars. The surface of all the elements of the disc is covered with 

 numerous close-set tubercles. The five ocular plates are cordate in form, and have mar- 

 ginal orbits. The abnormal deviation from the usual structure consists in the introduction 

 of two rows of small plates behind and between the normal discal elements. 



The base is concave and undulated (fig. 2 b), from the prominence of the inter- 

 ambulacra (fig. 2/) and the depressions formed by the ambulacra which radiate in straight 

 furrows from the peristome to the margin. The mouth lies at the bottom of a subcentral 

 depression. The peristome is central and shghtly five-lobed ; the tubercles are more con- 

 spicuous at the base than on the upper surface, and are closely placed upon the plates. 



The test is very thin, and the spines, which were preserved on one specimen, are 

 moderately long and needle-shaped. 



Affinities and differences. — The orbicular form and long anal valley liken this species 

 to EcJiinobrissus Woodioardii, Wr., but the convexity of the upper surface, the wideness 

 of the anal valley, the concavity of the base, and the slight tumidity of the sides, form a 

 group of characters of sufficient value to distinguish it from that congeneric species. It 

 resembles some of the small round varieties of Echinobrissus Hugii, Ag., but is readily 

 distinguished from them by the anal valley extending from the disc to the border, whereas 

 in Echinobrissus Hugii, Ag., there is always an undepressed portion of test between 

 the disc and upper limit of the anal valley. From all other OoHtic species it is so 

 entirely distinct that it is not likely to be mistaken for either of them. 



Locality and StratigrapUcal position. — This is a true Cornbrash urchin. I have 

 collected it from that " terrain" near Cirencester, and Miss Slatter found it in the same 

 rock near Fairford. Professor Phillips obtained his original type specimens from the 

 Cornbrash at Scarborough, and I have collected it out of the same bed. I am indebted to 

 my friend, John Leckenby, Esq., for a good series from that locality; and Edward Wood, Esq., 

 of Richmond, most liberally gave me the fine large specimen from Scarborough figured in 

 PI. XXV, fig. 2 «. I have received a very fine series of this species from my friend, the 

 Rev. W. A. Griesbach, which he collected from the Cornbrash at Rushden, Northampton- 

 shire ; these specimens have supplied abundant materials for the curious structure of the 



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