ECHINOIDEA. II. 



103 



From the description given by Agassi/, it is thus impossible to find Imw to distinguish fl. gibbosits 

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

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

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

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

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

 likewise onh- about half that in the anterior; further in cxpcrgifiis the inner ca. 7 pairs of pores in the 

 median (anterior) row 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 expcrgitns 29. — These differences look very good. If, however, we com- 

 pare the specimen of gibbosus of 20""" before nie with equal-sized cxpergihis, these differences become 

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

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

 small (in expcrgitns about 7). In the odd anterior amljulacrum I find in i^ibbosus 14 — 15 plates within 

 the fasciole, in expergitus 17 — 18. And in the specimens from the Challenger* in the Uritish 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' F'ig. 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 j^late 2. A.s, however, this figure gives in an)- ease a quite wrong 

 representation of the plates in the left posterior ambulacrum (I), it probably cannot be relied ujjou 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 pedicellariae (not seen in the Siboga -specimen) present a small difference (PI. X\'. 

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

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

 whereas the large tridentate pedieellariie (PI. X\'. Fig. 42) differ from those of expergitus in having 

 the edge in the outer part, wdiere 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 u])()n 

 this feature. Ophicephalous pedicellariiE were not met with in any of the si^eciraens 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 pedicellaritc 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 rightlv a^fain. Accordin"lv I must reyard //. i^ibbosus as a s\non\ni onl\- of //. expergitus; but 



