ECHINOIDEA. II. 



167 



justified in establishing genera based upon the coalescence of ambulacra which seems rather 



contradictory. 



The question of the two genera is, however, by no means solved by the remarks of Agassiz, 

 and the characters pointed out by him are of very slight value. The character that the genital plates 

 are a little longer in Brissopsis than in Toxobrissus can scarcely be taken to be meant seriously; at 

 least I am unable to see the generic difference in the extension of. the genital plates in the Figures 

 278 (Br.lyrifera) and 279 (T.pacificus) given by Agassiz (Op. cit. p. 191 and 193). Further as regards 

 the characters of the labrum and the five ambulacral plates included within the subanal fascicle Bris- 

 sopsis elongata agrees exactly with T. pacificus. (In the specimen represented in PI. 105. 4 (and Text- 

 figure 280) the labrum is abnormal, not reaching beyond the i. ambulacral plate of I. a; in the specimen 

 represented in PI. 103. 3 it is symmetrical, reaching the middle of the second ambulacral plate on both 

 sides, exactly as in Br. elongata). Also in the important character that the first ambulacral reaching 

 within the fascicle is the 7th, the two species agree (that it is so in T. pacificus is not mentioned 

 in the text, but it is distinctly seen in PI. 103. 3). Brissopsis elongata thus agrees with Toxobrissus 

 pacificus in three of its distinguishing characters, the form and extension of the labrum, number and 

 iiumero of ambulacral plates reaching within the subanal fascicle, and the confluent posterior petals, 1 

 but according to Agassiz 2 it cannot be referred to the genus Toxobrissus on account of the radical 

 difference* in the odd interambulacrum, viz. that in Toxobrissus the fourth abactinal series (of the 

 odd interambulacrum) is reduced to a single plate.3 Now this structure seems to be quite abnormal, 

 and it is not stated expressly to occur in all the specimens, though this might well have been worth 

 stating of a character thought to be so important; indeed, it does not seem to be so in the specimen 

 figured in PI. 103. 4 as far as can be seen it is here quite as usual, and in any case in the fig. 279 

 the fourth plate is seen to be double. The odd interambulacrum is thus evidently quite normal also 

 in Toxobrissus pacificiis and no character distinguishing this genus and Brissopsis is to be found 

 therein. If the species pacificus is really a Toxobrissus the Br. elongata then evidently also belongs 

 to that genus -- but its characters are not those pointed out by Agassiz. 



A short revision of the more important characters in the Itrissopsis-species must be given and 

 the grouping of the species after these characters shown, before the value of the genus Toxobrissus 

 can be appropriately discussed. The following characters must be taken as the more important, after 

 which generic divisions might possibly be made: the posterior petals, confluent or divergent; the 

 number of plates included within the subanal fascicle; the numero of the first plate reaching within 

 this fascicle ; the posterior extension of the labrum ; finally the structure of the globiferous pedicellariae. 

 Other features can scarcely come into consideration for" use eventually as a foundation for generic 

 divisions. 



1 Whether the pedicellarise of T, pacificus are like those of elongata, I cannot say. I have found on the specimens 

 examined in the U. S. National Museum only tridentate pedicellarise, which are very different from those of elongata, the 

 valves being rather flat, provided with numerous long, coarse, outwards directed teeth in the lower part of the -blade (in 

 larger specimens; having no complete valves I shall not give any figure of these). The more important globiferous pedi- 

 cellarise are unknown; it may well be supposed that they will prove to resemble those of elongata. 



2 I may expressly note that I do not maintain that Professor Agassiz has known the form established by me as 

 Br. elongata. In the present connection this is, however, without importance. 



3 This, I suppose, must be the character meant; at least I am unable to see what else it could be. 



