ECHINOIDEA. II. 



167 



justified in establishing genera based upon the coalescence of ambulacra> — which seeras rather 



contradictory. 



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

 and the characters pointed out by hini are of very shght vahie. The character that the genital piates 

 are a little longer in Bn'ssopsis 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 piates in the Figures 

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

 the characters of the labrum and the five ambulacral piates included within the subanal fasciole Bris- 

 sopsis elo7igata agrees exactly with T. pacificus. (In the specimen represented in PL 105. 4 (and Text- 

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

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

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

 within the fasciole is the jth, 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 

 numero of ambulacral piates reaching within the subanal fasciole, and the confluent posterior petals,' 

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

 differences 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 liere quite as usual, and in au}' case in the fig. 279 

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

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

 therein. If the species pacificus is really a Toxobrissus the Br. elongata tlien 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 Brissopsis-s^&CKs must be given and 

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

 can be appropriately discussed. The foUowing 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 piates included within the subanal fasciole; the numero of the first plate reaching within 

 this fasciole; the posterior extension of the labrum; finalh- the structure of the globiferous pedicellariæ. 

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

 divisions. 



■ Whether the pedicellariæ of T. pacificus are like those of elongala, I canuot say. I have found ou the specimens 

 examined in the U. S. National Museum only trideutate pedicellanæ, which are very differeiit 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- 

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



' I may expressly note that I do not maintain that Professor Agassiz has known the form estabhshed 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. 



