ECHINOIDEA. II. 



165 



ring below. The valves are much narrowed in the middle, the basal part being very narrow. The blade 

 is wide, deep in the middle and with sharp corners; the edge is strongly serrate almost down to the 

 articular surface. There is a small prolongation on the outermost of the three arches. — The tri- 

 phyllous pedicellariae do not differ from those of lyrifcra. 



After what has been pointed out here it is evident that the geographical and bathymetrical 

 distribution of Brissopsis lyrifcra has to be considerably restricted from what was previously generally 

 accepted. The species is known with certainty only from the European Seas, from Norway to the 

 Mediterranean, from the British Seas, the Faroe Islands, South of Iceland and Denmark Strait. The 

 bathymetrical distribution is from shallow water to ca. 200 fathoms. 1 It is, of course, quite possible 

 that it does really go down to considerably greater depths, like other sublittoral species of Echinoids, 

 as e. g. Echinus esculentus and Strongyloccntrotus drobachiensis. Likewise it is quite possible that it 

 will prove really to occur at the American side of the Atlantic; but we cannot accept that on the 

 previous statements; renewed investigations are needed in the light of the facts made known here. 

 That the small specimens from the Porcupine from 2090 2 fathoms (Wyv. Thomson. Porcupine - 

 Ech. p. 750) are not really Br. lyrifera, may be said with rather great certainty. 



The true Br. lyrifcra certainly shows considerable variation in the shape of the test, but by 

 no means so much as assumed by Agassiz, who has regarded the two very distinct species Br. alia 

 and atlantica (I cannot prove that Br. clongala was also confounded with lyrifera by Agassiz) as 

 variations only of lyrifcra.* The additional light said by Agassiz to be thrown on the changes 

 we may expect to find among Spatangoids of this group in one and the same species* by all the 

 very different looking specimens of Brissopsis lyrifcra from the Blake was, indeed, only additional 

 confusion. In the Revision df Echini p. 356 x\gassiz states of Brissopsis lyrifcra that with age the 

 lateral pairs of ambulacra gradually tend to unite, passing from a strictly Brissopsis outline (PI. XIX. f. 8) 

 to one considered hitherto characteristic of Toxobrissus (PL XIX. £9)*. And further (p. 355): The cha- 

 racter of continuity of the adjoining pairs of ambulacra, which Desor assigns to Toxobrissus as a 

 distinguishing feature, becomes more and more apparent according to the size of the specimens; so 

 much so, that we should place Brissopsis lyrifera, when young, in Brissopsis, but when full grown it 

 would most decidedly pass for a Toxobrissus . — It must be decidedly maintained that among the true 

 Brissopsis lyrifcra there is no tendency in the posterior petals to unite with age; they are in the full 

 grown specimens at least as distant as in the young ones, if not more. Even the figures given by 

 Agassiz himself in the <• Revision of Echini show sufficiently that the continuity of the posterior 

 petals is not a feature developed with age. PI. XIX. Fig. 9 is from a specimen 27-9 mm long, with very 

 confluent ambulacra; but in PL XXI. Fig. 2, representing a specimen of 49™"', the ambulacra do not 

 show the slightest tendency to unite. Evidently the specimen figured in PI. XIX 9 is a Br. atlantica 



' In IX. Report from the Danish Biological Station 1899, it is recorded from 210 fathoms from the Skagerrak. 



- In the Challenger-Ech p. 220 the greatest depth is stated to be 2435 fathoms. 



3 In the Preliminary Report on the Echini of the Albatross (Bull. Mus. Comp. Zool. XXXII. 1898. p. 82) Agassiz 

 expresses some doubt of the correctness of referring to Brissopsis such forms as the elongate type figured in the «Blake»- 

 Ech. PI. XXVI. Fig. 7, but in the «Panamic Deep Sea Echini^ p. 191 he again speaks of «the elongated and globular speci- 

 mens of the West Indian Brissopsis lyrifera*. 



