92 Dr. T. Wright on the Cassidulida? of the Oolites. 



two complete rows of tubercles arranged on the sides of the arese 

 (fig. 1 c), and two incomplete rows of tubercles internal to them, 

 which are neither so regular in their arrangement as the marginal 

 rows, nor do they extend beyond the lower half of the area?; the 

 single ambulacrum is perpendicular; the anterior pair arch gently 

 upwards and backwards, whilst the posterior pair rise forwards and 

 upwards for three parts of their course, and then make a short 

 curve round the anal opening, and terminate at the lateral border 

 thereof. The pairs of pores are disposed very closely together 

 in well-defined narrow avenues, which form distinct boundaries 

 between, the ambulacra and the interambulacra ; at the basal angle 

 the interambulacral are four times the width of the ambulacral 

 arese; the plates (fig. 1 d) are adorned with rather irregular rows of 

 very small tubercles varying in number from four to sixteen in a 

 row in different parts of the area ; the smooth areolae around the 

 tubercles are very superficial ; their circumference is encircled by 

 rows of microscopic granules : besides these granular circles, there 

 is scarcely any other sculpture on the plates, which gives a great 

 smoothness to the test of P. conoideus when compared with that of 

 P. semisulcatus. The anal opening (fig. 1 a) when compared with 

 that of the latter is proportionally small, occupying rather more 

 than the upper third of the single interambulacrum; the portion of 

 the area below the vent is flattened and slightly concave. The base 

 is covered with the oolitic matrix, which here forms a hard cry- 

 stalline rock, and cannot be removed without fracturing the test ; 

 enough is exposed however to show that the base is slightly 

 concave, and that the tubercles are much better developed in this 

 region than on the dorsal surface. The apical disc is absent, and 

 we know nothing of the spines. 



Affinities and differences. — This Urchin resembles P. semisul- 

 catus in its pentagonal form and in the number of the tubercles on 

 the areas; but is distinguished from that common species by the 

 greater prominence of the ambulacra, the smallness of the tuber- 

 cles, the superficiality of the areolae, the microscopic character of 

 the granulations, the elevated conoidal form of the test, and the 

 smallness of the anal opening; it is a rare species, the specimen 

 which we figure being the only one we have ever met with in our 

 researches ; a second specimen is in the cabinet of our friend John 

 Lycett, Esq. 



Locality and stratigraphical range. — I found this Urchin in the 

 Pea-grit of Crickley Hill. Mr. Lycett's specimen came from 

 the Inferior Oolite near Stroud. 



Pygaster Morrisii, Wright, n. sp. PI. IV. fig. 1 a-d. 



Test much depressed and pentagonal, basal angle tumid ; ambu- 

 lacra wide, prominent and convex, with six rows of tubercles; 



