KCHINOIDEA. II. 



103 



From the description given by A gas si z it is thus impossible to find how to distinguish H.gibbosus 

 from expergitus. A comparison of the figures seems to give a somewhat better result, the petals and the odd 

 ambulacrum showing some difference: In the specimen of gibbosus figured by Agassiz in PI. XX. 5 and 



i) (ca. 30""" in length) the posterior petals are only a little shorter than the anterior ones, and the number 

 of pores in both petals is almost the same. In the largest specimen of expergitus (37""") the posterior 

 petals are only half as long as the anterior ones and the number of pores in the posterior petals is 

 likewise only about half that in the anterior; further in expergitus the inner ca. 7 pairs of pores in the 

 median (anterior) row T of the anterior petals are small, in gibbosus, according to Fig. 9, they are all large 

 and conjugated. The number of plates in the odd ambulacrum within the fasciole is in gibbosus (ac- 

 cording to Fig. 9) ca. 18, in expergitus 29. — These differences look very good. If, however, we com- 

 pare the specimen of gibbosus of 20 mm before me with equal-sized expergitus, these differences become 

 very slight. In both I find the anterior petals twice as long as the posterior and with the double 

 number of pairs of pores. In gibbosus I find the 4 inner pairs in the median row of the anterior petals 

 small (in expergitus about 7). In the odd anterior ambulacrum I find in gibbosus 14 — 15 plates within 

 the fasciole, in expergitus 17— iS. And in the specimens from the Challenger in the British Museum 

 the posterior petals are only about half as long as the anterior ones, and the inner 5 — 7 pores of the 

 inner series of the anterior petals are small, not conjugate. No specimen in the British Museum 

 corresponds to the Fig. 9. PI. XX of the < Challenger»-Echini. These differences thus become so slight 

 that they seem rather inappropriate for distinguishing two species thereby. But other distinguishing 

 characters do not seem to be found in the structure of the test. The fasciole is alike in shape, like- 

 wise the spines. To be sure the labrum, according to Agassiz' Fig. 6 would seem to give some differ- 

 ence: Its posterior end reaches on the right side the middle of plate 3 in the adjoining ambulacrum, 

 on the left side to the middle of plate 2. As, however, this figure gives in any case a quite wrong 

 representation of the plates in the left posterior ambulacrum (I), it probably cannot be relied upon for 

 the right side either, the more so as in the specimens in the British Museum the labrum reaches only 

 to the middle of the second ambulacral plates of the adjoining series. The specimen from the Siboga» 

 likewise agrees exactly with equal-sized expergitus in this respect. — The number of buccal plates 

 and the form of the peristome is the same in both of them. The tube-feet and spicules are alike. - 

 The globiferous pedicellarise (not seen in the Siboga -specimen) present a small difference (PI. XV. 

 Fig. 46) : the blade is more elongate, with four teeth around the terminal opening, and the basal part 

 is narrower than in expergitus. The rostrate pedicellarise do not present any reliable differences, 

 whereas the large tridentate pedicellarise (PI. XY. Fig. 42) differ from those of expergitus in having 

 the edge in the outer part, where the valves join, regularly serrate — but in view of only one speci- 

 men of this kind having been found in expergitus, it does not seem reasonable to lay any stress upon 

 this feature. Ophicephalous pedicellarise were not met with in any of the specimens of gibbosus exam- 

 ined. There seems then not to be a single reliable difference of any reasonable importance by which 

 to distinguish gibbosus from expergitus (— also in the structure of the globiferous pedicellariae there 

 is some variation in expergitus, as pointed out above, p. 100, so that they present no reliable difference 

 either — ). If specimens of both species were put together, I think it would be impossible to separate 

 them rightly again. Accordinglv I must regard //. gibbosus as a synonym only of //. expergitus: but 



