240 ACROSALENIA. 



much larger than the three others (fig. 3 /) ; the madreporiform body is very small, and 

 occupies as usual the right anterior genital plate; a few small granules form central 

 clusters on the pairs of genitals, and similar granules dot the surface of the small oculars 

 (fig. 3/). 



The mouth opening is nearly half the diameter of the test (fig. 3 b) ; the peristome is 

 decagonal, and divided by small notches into nearly equal-sized lobes ; the incisions are 

 not deep, and the margin is reflected overall the angles (fig. 3/). 



Affinities and differences. — This species is distinguished by its small size and depressed 

 test, the extreme regularity of its tubercles, the radiated appearance of the upper surface, 

 the apical disc having the sur-anal plate single, and the vent of a triangular form ; these cha- 

 racters serve to distinguish it from all its other English congeners. It resembles A. aspera in 

 many of its general characters, but that species has undulated ambulacral areas with close-set 

 tubercles and the sur-anal plate composed of two pieces ; it is so entirely distinct from all 

 other forms of the genus at present known, that it is unnecessary to pursue a comparison 

 with them. 



Locality and StraiigrajoJiical position. — I have collected two specimens of this urchin 

 in the Pea grit. Inferior OoHte, at Crickley Hill, and in the yellow clay resting on the 

 Stonesfield Slate at Sevenhampton, with Anahacia orhuUtes,Pecten vac/ans, Ostrea acuminata, 

 and other Great Oolite fossils. I have likewise found it in the Great Oohte at Sham Castle, 

 near Bath. Mr. Lycett has collected it from the Great Oolite of Minchinhampton 

 Common, where it is small in size and rare. It is abundant in the Forest Marble and 

 Cornbrash near Chippenham, with Avicula echinata, Sow., whence my finest specimens 

 were collected by Mr. William Buy. It is found, likewise, in the Forest Marble 

 and Cornbrash near Cirencester; indeed, it may be considered an abundant fossil 

 in the English Cornbrash, but I have seen no specimens at all equal in their preservation 

 and beauty to those found in Wiltshire. 



In Switzerland it was collected by M. Strohmeyer from the marls containing Ostrea 

 acuminata, in the canton of Soleure. In France it has been found in the Great Oohte of 

 Ranville, Calvados, by Professor Deslongchamps, and in the upper beds of the Bathonien 

 etage in the environs of Chatel-Censoir, by M. Cotteau. 



AcRosALENiA LowEANA, Wright, nov. sp. PI. XVII, fig. 4 a, h, c, d. 



Test circular, much depressed ; ambulacral areas narrow and sinuous, with marginal 

 rows of very small wide-set tubercles ; inter-ambulacral areas with six primary tubercles 

 in each of the two rows, of which the two equatorial pairs are very large ; apical disc of 

 moderate size, sur-amal plate composed of three pieces ; primary tubercles near the disc 

 very small. 



