342 



ECHINODERMS OF THE BRITISH ISLES 



shortened (Fig. 202, 2). Only 2 genital pores present, situated 

 in the plate joining the anterior ambulacrum ; other genital 

 plates camiot be distinguished with certainty. The genital pores 

 are covered by long genital papillae. Spines numerous., small and 





Fig. 202. — Plexechinus hirsutus ; naked test, from below (1), from above (2), 

 and in side view (3). x 1-5. (After Th. Mortensen, "/ngroZ/" Ech., ii.) 



slender, curved, arranged without distinct order. The globiferous 

 pedicellariae (Fig. 203, 2) are rather pecuUar, the valves having 

 a large, round terminal opening with slightly serrate edge. The 

 other pedicellariae very simple. Colour in life probably violet. 

 Largest size recorded, 20 mm. length. 



Fig. 203. — Valves of globiferous pedicellariae of Urechinus naresianus (1) 

 and Plexechinus hirsutus (2). 1. xl25; 2. x 175. (After Th. Mortensen, 

 " Ingolf' Ech., ii.) 



Biology and development unknown. From the young 

 Urechinus naresianus, in which the periproct is likewise above 

 the ambitus, this species is easily distinguished by the 

 different outline of the test (the sternum of the latter forming 

 no keel), by its shortened frontal ambulacrum, and the quite 

 different globiferous pedicellariae (Fig. 203, 1). 



