458 ADDITIONAL NOTES 



Test circular, depressed ; ambulacral areas wide, with two rows of small tubercles on 

 the margin of the area, set moderately distant apart ; poriferous zones narrow ; pairs 

 of pores superimposed in groups of threes; inter-ambulacral areas with two rows of 

 primary tubercles on the centre of the plates, and two rows of secondary tubercles 

 internal to the primaries, which extend from the base and sides above the equator; 

 areolae wide, encircled by granules which likewise cover the surface of the plates. Spines 

 long, slender, and needle-shaped; surface covered with fine, longitudinal lines. 



Dimensions. — Height unknown ; transverse diameter, one inch and two tenths. 



Description, — The specimens of this urchin hitherto found are so much crushed and 

 broken that it is impossible to make an accurate description of the species. The test 

 is circular and depressed ; the ambulacra are one third the width of the inter-ambulacra, 

 and provided with two rows of small tubercles, which occupy the margin of the area ; 

 they are placed at a distance equal to the diameter of their areolae apart from each other, 

 and a delicate, zigzag line of small granules descends down the centre of the area ; 

 the poriferous zones are narrow, and in their upper part the pairs of holes manifest 

 a disposition to a trigeminal arrangement, the inclination of the rows being upwards 

 and outwards, the reverse of the direction in the genus Pedina. There are four 

 or five pairs of holes opposite one large plate. The inter-ambulacral areas are three times 

 as wide as the ambulacra at the circumference ; one complete row of primary tubercles 

 occupies the centre of the plates, and one incomplete row the inner portion thereof; 

 the latter extend from the base and sides to two plates above the circumference. The 

 primary tubercles at the equator have prominent bosses, which diminish in size on the 

 upper surface ; the areolae are wide, smooth, well defined, and confluent above and below, 

 laterally they are bounded by semicircles of small granules ; at the zonal side of the plates 

 there are three or four rows of the same-sized granules, and they likewise form circles 

 around the incomplete rows on the centre of the area. The spines are slender and 

 needle-shaped ; the milled ring is prominent, and the surface of the stem covered with 

 well-marked, longitudinal lines. All the specimens I have seen lie on their base on the 

 matrix, and in none of them is the apical disc preserved. 



Affinities and differences. — This urchin is much larger than Hemipedina Bowerhanhii, 

 Wr., which was collected from the same zone of the Lower Lias, near Lyme Regis. 

 It resembles Hemipedina seriate, Leym. (PI. IX, fig. 3 a), from the Lower Lias of 

 France, but the inner row of tubercles in the inter-ambulacra are more developed and have 

 a greater extension in that species. 



Locality/ and Stratic/raphical position. — This urchin was discovered by Mr. R. Tomes 



