Dr. T. Wright on the Cassidulidas of the Oolites. 185 



two complete rows of tubercle* arranged on the sides ofthearese 



! e) s ami two incomplete rows of tubercles internal to them, 



w hu-ii are neither so regular in their arrangement as the marginal 



. 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 forward 

 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; attheba>al angle 

 the interambulacral are four times the width of the ambulacral 

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

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

 in different parts of the area; the smooth areola? around the 

 tubercles arc 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. conuideus 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 porticn 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 tubercle- on 

 the area); but is distinguished from that common species by the 

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

 cles, the superficiality of the areola?, 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, !' 



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. VIII. fig. 1 a-d. 



much depressed and pentagonal, basal angk tumid; ambu- 

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



