156 Dr. T. Wright on the Cidaridae of the Oolites. 



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

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

 rfaris 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 areae is a good character for Hemici- 

 da?'is. 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 Kiddington, 

 Oxfordshire, in slabs of Great Oolite. From these facts we infer 

 that this large Acrosalenian had not only a considerable strati- 

 graphical range, but likewise that the species was very abundant. 



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



Test hemispherical, depressed, circumference subpentagonal ; 

 ambulacral areae prominent, having a double series of small 

 tubercles ; interambulacral areae with two ranges of large tu- 

 bercles ; mammillary eminences of both areae conical and pro- 

 jecting ; tubercles of the interambulacral areae 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 areae 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 areae, sending out lateral 

 branches which inclose the areolae of the tubercles for about two- 

 thirds of their circumference, leaving the areolae open to the 

 poriferous avenues. The interambulacral areae arc nearly three 



