REPORT ON THE ECHINOIDEA. 151 



ambulacral system at the abactinal pole, the flat aetinostome with its internal rudiments of 

 supports for teeth still existing, are all features which we do not associate with the 

 group of Spatangoids. I have already called attention to the general similarity of this 

 genus with Galerites; in the latter we still find teeth, smaller ambulacral plates, the same 

 aetinostome, however, only more Clj'peastroid ; and the arrangement of the tubercles 

 (primary, secondary, and miliary) is very similar in Galerites to that of the tubercles of 

 the present group. 



The outline of the test of this species when seen from the apical pole on the actinal 

 surface is elliptical, the anterior and posterior extremities equally rounded (PL XXXV. 

 figs. 1, 3). The aetinostome is placed somewhat in advance of the centre, the apical 

 system and apex are coincident, slightly posterior. The actinal surface is flat, slightly 

 sunken from near the ambitus; the ambitus forms a sharp curve between the actinal 

 surface and the sides of the test (PI. XXXV. fig. 2) ; owing to the extreme tenuity of 

 the test, it is difficult to see its outline when seen in profile, the mere weight of 

 the test forming large folds extending from the apex to the ambitus (PI. XXXV. figs. 

 1, 2, 4). The outline when fully expanded, probably resembled that of Cystechinus 

 ivyvillii, only at the ambitus the test is less gibbous, the posterior extremity more rounded 

 and sloping more vertically, and the anterior extremity sloping quite uniformly with but 

 a slight re-entering angle from the rounded apex to the ambitus. 



It is difiicult in the ill-shaped test, looking like an old felt hat, figured on Plate 

 XXXV. fig. 4, to recognise the outline of a graceful test such as this species undoubtedly 

 had, judging from that of the allied Cystechinus ivyvillii. 



The anal system in this species is placed well above the actinal surface flush with the 

 test (PI. XXXV. fig. 2), and there is no trace of a hood or rudimentary abactinal beak as 

 in Cystechinus wyvillii. 



This is the only Spatangoid thus far known, which can evidently expand or contract 

 its test. This was known in the Diadematidse (Astro^yyga) among the regular Echiuids, 

 previous to the discovery of the Echinothuridse among the recent forms; in these the test 

 is, as I have said, capable of very great expansion and contraction and extensive change 

 of shape. The lapping of the coronal plates of some Sjaatangoids, to which Ludwig' has 

 called attention, is undoulstedly an ajjparatus adapted within narrower limits for the same 

 purpose. 



Station 153. February 14, 1874. Lat. 65° 42' S., long. 79' 49' E.; 1675 fathoms; 

 mud. 



Station 298. November 17, 1875. Lat. 34° 7' S., long. 73' 56' W.; 2225 fathoms; 

 bottom temperature, 1'3° C. ; grey mud. 



Station 299. December 14, 1875. Lat. 33' 31' S., long. 74° 43' W.; 2160 fathoms; 

 bottom temperature, 1'1° C. ; grey mud. 



' H. LucUvig, Morphologie der Echmodenuen, 1877-79, vol. iii. \y[}. 131-140. 



