from the Lias and Oulitfs. 33 



face of both is covered with minute granules nearly as large as 

 those which adorn the other parts of the test. The madn 

 form tubercle makes a distinct elevation on the surface of the 

 single plate, and the anal aperture is transversely oblong ; the 

 base is flat, the mouth-opening is small, and its margin is divided 

 into ten nearly equal-sized lobes ; the spines are unknown. 



Affinities and differences. In its general outline and depressed 

 upper surface, with the pedal pores in nearly a single file, this 

 little Urchin resembles a Diadema ; from that group however it 

 is distinguished by the rudimentary condition of the ambulacral 

 tubercles, and the absence of crenulations from the summits of 

 the mammillary eminences. It is distinguished from P. Bakeri 

 by having small primary tubercles set more closely together, and 

 in having a greater number in each row. From P. aspera it is 

 known by having the upper surface more depressed, the pedal 

 pores separated by a moniliform line of granules, and in the 

 absence of secondary tubercles. It has a strong resemblance at 

 a first glance to Diadema Moorei, but an examination with the 

 lens at once discloses the points of difference, which are these : 

 the ambulacral areas in Pedina Etheridgii have imperforate gra- 

 nules on their upper parts, whilst in Diadema Mourei there are 

 perforated tubercles; the moniliform line between the pedal 

 pores in P. Etheridgii is absent in D. Moorei-, the mouth- 

 opening is likewise much smaller in P Etheridgii than it is in 

 D. Moorei. 



Locality and stratigraphical range. P. Etheridgii has been 

 collected from the marlstone of Bredon Hill, Gloucestershire. 

 Mr. Moore found it in the Upper Lias of Ilminster, and we have 

 collected several specimens from the Pea-grit (Inferior Oolite) 

 of Crickley and Leckhampton Hills, but have never seen a 

 trace of this species in any of the upper beds ; it seems there- 

 fore to have a limited vertical range between the marlstone and 

 the basement-beds of the Inferior Oolite, and is one of the few 

 species which lived in the Liassic and Oolitic seas. 



We dedicate this species to our friend Mr. Etheridge, of the 

 Bristol Museum, who has kindly assisted us in comparing our 

 specimens with the fine series of Echinoderms under his care, 

 and has likewise otherwise aided us in the most friendly manner 

 in working out the subjects of these memoirs. 



Genus POLYCYPHUS, Agassiz. 



Small Urchins having a subglobular form ; the upper surface 

 of the test is covered with numerous small imperforate tubercles 

 of a very uniform size ; the base and basal angle are furnished 

 with several tubercles of a size disproportionately large when com- 

 pared with those of the upper surface ; the pedal pores are dis 



VOL. II. D 



