154 HEMIPEDINA. 



the same rock. Hemipedina perforata and Hemipedina Waterhousei having two rows, and 

 Hemipedina Bonei six rows of tubercles in this region. 



Locality and StratigrapJdcal position. — The only specimen I have seen of this species 

 I collected from the Pea Grit at Crickley Hill, along with Hemipedina perforata, Acrosa- 

 lenia Lycettii, PolycypJius Deslongcliampsii, and Pseudodiadema depressum. 



Hemipedina Waterhousei, WrigJit. PL X, fig. 4 a, h, c, d, e. 



Hemipedina Waterhousei. Wright, Annals and Magazine of Natural History, 2d series, 



vol.xvi, p. 98. 



Test small, pentagonal, rather inflated at the sides ; ambulacral areas with two rows of 

 small tubercles extending from the peristome to the disc ; inter-ambulacral areas with two 

 rows of tubercles, eight in a row ; scrobicular circles neatly defined ; mouth opening small ; 

 apical disc narrow and prominent. 



Dimensions. — Height, seven twentieths of an inch ; transverse diameter, half an inch. 



Description. — This is a small, pentagonal, inflated species, having the ambulacral areas 

 with two rows of tubercles, nearly as large as those of the inter-ambulacral ; there are from 

 twelve to thirteen tubercles in each row, which are placed further apart than those of 

 H. tetragramma, each tubercle being surrounded by small, scattered granules (fig. 4> c, e) ; 

 the poriferous zones are narrow and straight (fig. 4 e), and the septa are slightly elevated 

 on the surface ; there are four pairs of pores opposite each of the large plates. 



The inter-ambulacral areas are not quite twice the width of the ambulacral ; they are oc- 

 cupied by two rows of primary tubercles, about nine in each row, which have slightly elevated 

 bosses, surmounted by small tubercles ; the base of the boss is closely encircled by small 

 granules (fig. 4 e), which form complete scrobicular circles around them ; each plate has 

 one row of granules between the tubercles and the zones, and two rows of granules between 

 the tubercles and centro-sutural line (fig. 4 e). 



The apical disc is well preserved in both my specimens (fig. 4 3, d) ; the genital 

 plates have a heptagonal form, the largest side being placed towards the anal opening ; 

 they are perforated at a short distance from the apex, and two or three granules are 

 developed on the surface ; the right antero -lateral plate is a little larger than the others, 

 and supports, as usual, a small, spongy, madreporiform body ; the ocular plates are small 

 and pentagonal ; the boles are perforated near the centre of each ; the disc forms a slight, 

 ring-like prominence at the vertex of the test, and the anal opening is circular. 



