FROM THE INFERIOR OOLITE. 149 



is large (fig. 5f/); the ovarial plates are widely rhomboidal (fig. 5 d) ; the oculars 

 are small and heart-shaped ; and the surface of both is covered with minute granules, 

 nearly as large as those which adorn other parts of the test. The madreporiform tubercle 

 makes a distinct elevation on the surface of the right anterolateral plate (fig. 5 d) ; the 

 anal aperture is transversely oblong; the base is flat, the mouth opening small, and 

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



Affinities and differences. — In its general outline, depressed upper surface, and uni- 

 geminal pores, this little urchin resembles a Pseudodiadema. 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 bosses. It is distinguished from Hemipe- 

 dina Bakeri by having small primary tubercles set more closely together, and in having a 

 greater number in each row. From Pedina rotata it is known by having unigeminal 

 pores, the upper surface more depressed, the pedal pores separated by a moniliform line of 

 granules, and in the absence of secondary tubercles. At a first glance, it has a strong 

 resemblance to Pseudodiadema Mooreii, but an examination with the lens at once discloses 

 the points of difference, which are these : the ambulacral areas in Hemipedina Etheridgii 

 have imperforate granules on their upper parts, whilst in Pseudodiadema Mooreii they are 

 perforated tubercles ; the moniliform line between the pedal pores in Hemipedina Etheridgii 

 is absent in Pseudodiadema Mooreii ; the mouth opening is likewise much smaller in Hemi- 

 pedina Etheridgii. 



Locality and Stratigraphical position. — This species has been found in the Upper 

 Lias of Gloucestershire, and in the Upper Lias near Ilminster, Somersetshire, associated 

 with Ammonites {Walcotii) bifrons, Brug. ; Ammonites serpentinus, Schloth. ; Ammonites 

 annulatus, Sow. ; and other Upper Liassic forms of Mollusca and Radiata. It is a very 

 rare urchin, and is seldom found in a good state of preservation. Professor Deslongchamps 

 has collected the same species in " le Lias superieur de May et Fontaine — Etoupefour, 

 Calvados." I dedicate this species to my friend Robert Etheridge, Esq., F.R.S.E., of the 

 Bristol Museum, who has kindly assisted me in comparing my specimens with the fine 

 series of Echinoderms under his care, and who has likewise otherwise aided me in the 

 most friendly manner, in working out the subjects of this Monograph. 



B. Species from the Inferior Oolite. 

 Hemipedina Bakeri, Wright. PI. X, fig. 1 a, b, c, d, e,f. 



Pedina Bakeri. Wright, Annals and Magazine of Natural History, lid series, 



vol. xiii, p. 312, pi. II, fig. 4. 

 Hemidiadema Bakeri. Desor, Synopsis des Echinides Fossiles, p. 58. 



