181 Dr. T. Wright on the CassidulitUe of the Oolites. 



Affinities and differences. — P. semisulcatus most nearly resem- 

 bles P. umbrella ; we have before us specimens which are well 

 represented by Agassix'a figure ; but the loss of the tubercles from 

 fcbe Swiss specimen leaves the question of their identity an open 

 one, as we regard the Special form of sculpture of the test 

 a most important specific character. P. semtsukatus differs from 

 P. Morrim in having narrower ambulacra and fewer tubercles 

 on both ares; the size and number of the tubercles and the 

 depression of the test afford distinguishing characters between 

 it and P. conoideus. 



Locality and straligraphical range. — This Urchin is abundant 

 in the lower ferruginous beds, "the Pea-grit" of the Inferior 

 Oolite at Crickley, Birdlip, and Leckhampton Hills, and in the 

 shelly freestone of the same localities, and I have collected small 

 specimens from the planking beds of the Great Oolite at Min- 

 chinhampton ; in Yorkshire it was collected by Mr. Phillips * 

 from the Coralline Oolite of Malton and Scarborough. In the 

 Pea-grit it is associated with Diadema depressum, Hyboclypus 

 agariciformis, Rhynconella Wrightii, Thecidea triangularis, Tere- 

 bratula simplex, and Ter. plicata. 



History. — This species was figured by Mr. Phillips, but not 

 described, in his * Geology of Yorkshire/ The absence of typical 

 foreign specimens does not enable us to decide whether the Ga- 

 lerites umbrella of Lamarck is identical with Mr. Phillips's spe- 

 cies. The fine and nearly perfect specimen before me has been 

 figured by Professor Forbes for the 4th Decade of his admirable 

 ' Illustrations of British Fossils ;' for this reason we have not 

 given a drawing of the species. 



Pygaster conoideus, Wright, n. sp. PI. VII. fig. 1 a-d. 



Test conoidal, with a pentagonal circumference ; ambulacra nar- 

 row and prominent, with two rows of marginal tubercles and 

 two imperfect rows of central tubercles; interambulacra four 

 times the width of the ambulacra, with very small tubercles 

 and a scanty granulation on the surface of the plates ; anal 

 opening comparatively small, occupying the upper third of the 

 single interambulacrum ; base flat. 



Height 1 inch and f^ths, antero-posterior diameter 2 inches 

 and ,/^ths, transverse diameter 2 inches and T ^ths. 



Description. — This Urchin is remarkable for its conoidal form, 

 the anterior and lateral walls of the test forming angles of from 

 50° to 55° with the base, and the posterior wall an angle of about 

 42° (fig. 1 h). The ambulacra arc narrow and prominent, having 



* (ifol. of Yorkshire. Part 1. p. 1 J 7 



