Dr. T. Wright on the Cidaridse of the Oolites. 263 



test, the structure of the ambulacra and poriferous avenues, that 

 it was not until we had obtained specimens with the apical disc 

 preserved that we were satisfied of its being an Acrosalenia, of 

 which it certainly forms the finest species. The genera Hemici- 

 daris and Acrosalenia have so many characters in common, which 

 are almost always well-preserved, and so few that are special, and 

 which are for the most part either broken or absent, that it is 

 difficult to decide upon the genus unless the apical disc is more 

 or less preserved ; it is for this reason we conjecture that so few 

 Acrosalenia have been hitherto catalogued from the Oolites, most 

 of the species having been erroneously referred to other genera. 

 The development of from four to six larger mammillated tubercles 

 at the base of the ambulacral area? is a good character for Hemici- 

 daris. In A. hemicidaroides the tubercles in this region are well 

 developed, but are not so well defined as in Hemicidaris. When 

 doubts exist, they can only be solved by the discovery of the 

 apical disc with its supra-anal plate. 



Locality and stratigraphical range. — I have collected this beau- 

 tiful Urchin from the upper beds of the Inferior Oolite at Leck- 

 hampton, and the Rev. P. B. Brodie found it with its spines 

 attached in the same zone at Selsley Hill. It is found in the 

 planking beds of the Great Oolite at Minchinhampton, and in 

 the Cornbrash near Chippenham. Several fine specimens with 

 the spines attached to the test were obtained from the Forest 

 marble near Malmsbury in Wilts, which are now in the British 

 Museum and the Museum of Economic Geology, and several 

 private cabinets. We have the same species from Kidding- 

 ton, Oxfordshire, in slabs of Great Oolite. From these facts 

 we infer that this large Acrosalenian had not only a considerable 

 stratigraphical range, but likewise that the species was very 

 abundant. 



Acrosalenia Lycetti, Wright, n. s. PI. XL fig. 2 a, b, c, d. 



Test hemispherical, depressed, circumference subpentagonal ; 

 ambulacral arese prominent, having a double series of small 

 tubercles ; interambulacral arese with two ranges of large tu- 

 bercles ; mammillary eminences of both arese conical and pro- 

 jecting ; tubercles of the interambulacral arese disproportion- 

 ately small. 



Height half an inch, transverse diameter 1 inch. 



Description. — This Urchin resembles A. hemicidaroides in 

 many of its characters, but presents others which justify its sepa- 

 ration from that species. The ambulacral arese are straight, pro- 

 minent, and furnished with a double row of small well-developed 

 tubercles, about' twelve in each row ; a zigzag line of small gra- 

 nules descends down the centre of the arese, sending out lateral 



