ECHINOIDEA 319 



Biology unknown. Development unknown, but the large size 

 of the female genital pores indicates large, yolky eggs and there- 

 fore direct development, without a pelagic larval stage. 



A single specimen of this species was dredged by the 

 *' Porcupine " at the mouth of the English Channel (48° 31' N., 

 10° 3' W., 1240 m.) ; it is thus not found within the British area 

 proper, but as there is every reason to expect that it will occur 

 also off the west coasts, and since the species is included in the 

 lists of British echinoderms given by Hoyle and Bell, it has 

 been thought desirable to include it in the present work. It is 

 known elsewhere from off the coast of Portugal and Morocco, and 

 from the Mediterranean ; further it occurs in the West Indian 

 seas (from where the species was first known, and where it 

 appears to be rather common). Bathymetrical distribution ca. 

 145-1240 m. 



V. Order. Spatangoidea 



Test elongate, not flattened. Mouth anterior, anal opening 

 posterior. No gills or gill-cuts at peristomial edge of test. No 

 internal supporting system of pillars. No dental apparatus. 

 Ambulacra simple or petaloid on the upper side and usually 

 slightly widened at the mouth. Posterior interambulacrum 

 different from the other interambulacra on the oral side, usually 

 more or less modified so as to form a " sternum " or " plastron " ; 

 the first plate of the posterior interambulacrum often specially 

 developed into a prominent "labrum". Tubercles perforate. 

 Spines of various length, those on the plastron often widened into 

 s spade-shape. Often distinct bands of very small, close-set 

 spines, the '" fascioles ". Tube-feet confined to the ambulacra, 

 usually very diversified, those around the peristome penicillate. 

 Pedicellariae often very conspicuous ; besides the usual four 

 types, a fifth form, the " rostrate " pedicellariae (Fig. 199, 3), 

 also occurs. Sphseridia present, not in grooves. 



This large order is divided into two suborders, both of which 

 are represented in the British seas. 



Key to the suborders of the Spatangoidea. 

 First pair of plates in posterior interambulacrum placed side by 



side ( " amphisternous " ) (Fig. 185, 1) . I. Amphisternata 



First pair of plates in posterior interambulacrum placed one behind 



the other (" meridosternous ") (Fig. 185, 2) II. Meridosternata 



I. Suborder. Amphisternata Loven. 



First pair of plates in posterior interambulacrum placed side 

 by side, not one behind the other, often much larger than the 



