ECHINOIDEA. II. gi 



age . This, indeed, seems highly improbable.' The smaller specimen (2o mm ) has its genital pores well 

 developed, and thus cannot be regarded as a quite immature specimen. But a change so enormous as 

 would be necessary to make the short form like the elongated during its growth from a size of 20""" 

 to 43""" would he quite unparalleled among Echiuoids - and that change should even take place 

 after the animal had become sexually ripe. Adding hereto that the smaller, short form is from the 

 Atlantic, whereas the large, elongated form proceeds from the Arafura Sea (Kee Islands, «Chall. 

 St. 191); that the latter closely resembles the pacific species A. fulva, and further that a specimen of 

 34" ,m length from the Iugolf agrees with the short form in the shape of the lest, we may safely 

 conclude that the elongated form figured in the Challenger -Echinoidea is not ./. rostrata; if it is 

 identical with A .fulva is not so certain, perhaps it will prove to be a new species. (Comp. below p. 94). 



The specimens from the Iugolf agree very closely in the shape of the test with the figures 

 given by Wyv. Thomson and with the figures of the short specimen given in the Challenger - 

 Echinoidea; there can thus be 110 doubt of their identity with A. rostrata, except in case there should 

 turn out to be more than one species among the short forms. Also the locality agrees: the specimens 

 of the Iugolf were taken in the Davis Strait, the type-specimen of Wyv. Thomson between Cape 

 Cod and Cape Hatteras (Chall. St. 45). 2 The locality where it was taken by the Valorous -Expedition 

 (59 10' Eat. N. 50 25' Long. W. 1750 fathoms), is also in the Davis Strait, and rather near the Ingolf» 

 stations. 



The largest of the specimens taken by the Iugolf is 34""" long, ij n < m broad and 18""" high. 

 Another specimen is 25™'" long, i2 mm broad and 13""" high. (PI. V. Figs. 8 — 10, 15, 20, 22.) — Concerning 

 the shape of the test it is to be remarked that it is a little compressed in the posterior part, the 

 actiual plastron forming a slight keel. The front end is, as pointed out by Wyv. Thomson and 

 Agassiz, rather abruptly cut; but the anterior edge forms a narrow, almost vertical ridge whose 

 lower corners are rather prominent. Along the lower edge of this ridge the fasciole passes. The ante- 

 rior ambulacrum is somewhat deepened almost down to the vertical ridge; only the plates in this 

 deepened part carry large tube-feet. According to Agassiz (Chall. p. 194) the 

 posterior extremity turns upwards (in the short form). In his figures that is not 

 seen very distinctly, to say the least, and in my specimens I do not see it either. 

 Perhaps this ought to have been said of the large specimen; in A. fulva it is a 

 distinct feature, as shown by Agassiz in his Panamic Deep-Sea Echini >, PL 61. 3; 

 — on this occasion (p. 194) it is otherwise stated that . the posterior extremity of 



A. rostrata slopes quite gradually to meet the rounded anal extremity . Fig. 15- Apical system 



of Aeropsis rostrata. 

 The apical system is described as compact, the madreporic body occu- 

 pying the greater part of the inner edges of the anterior genital plates and of the eight posterior 

 plates-. This would give a composition of the apical system of no less than eleven plates, which is 

 evidently wrong, 9 plates, as is well known, being the usual number of plates in the apical system 



1 Duncan evidently also doubted the identity of the two forms, as appears from his remark: It is very important 

 that separate descriptions of the specimens from Davis Straits and the remote Arafura Sea should be presented to science . 

 (Revision, p. 272). 



2 «The Atlantic , loc. cit. Agassiz does not mention this locality in his Report on the Echinoidea, only Bay of 

 Biscay and Coast of Spain < besides the wrongly cited St. 191. 



