84 



ECHINOIDEA. I. 



resemblance in tlie stnicture of the test to A. iiioiiilis (comp. Chall. Ech. PL VIL Fig. 15 witli PI. XVIII. 

 Fig. 12. a in Des or: -Synopsis des Échinides fossiles*, or with PL XV. Fig. 11 in Agassiz and Desor: 

 «Catalogue raisonné»), and so I sliall establish no new genns for this form, bnt for the present let it 

 remain in the genus Arbacina. 



Trigonocidaris albida A. Agass. The globiferous pedicellariæ (PL VII. Fig. 31) chiefly as in 

 Arbacina^ a single cross-beam may, however, be found between the edges of the blade; the poison 

 gland large reaching almost to the articular surface. I have found no tridentate pedicellariæ in the 

 specimen before me. The ophicephalous pedicellariæ are short-necked , with no special peculiarities. 

 The triphyllous pedicellariæ are very small and of a rather peculiar form (PL VII. Fig. 23). The blade 

 is rather broad, round, the edge exceedingly finely serrate (the serrations can only be seen under 

 rather higher magnifying powers than those under which the figure is drawn). The spicules are biha- 

 mate (PL VII. Fig. 28), very few. The spines are constructed after the same type as those of Hypsi- 

 ecJiinus and Prioncchinus\ the primary spines round the mouth are curved. 



The difference between Trigonocidaris and Prioneclmius seems to be very slight. The most 

 important one seems to be that Prionechinus has no such grooves in the test as those of Trigonocidaris. 

 To be sure, Agassiz does not mention the feature at all, and neither have I examined myself how 

 the facts are in this respect; but I think that the very faet of none of us having observed such grooves, 

 may be taken as a proof that they, at all events, are only slightly developed; if this was not the case 

 they would certainly have been observed. 



Whether Trigonocidaris monoliiii A. Ag. is a real Trigonocidaris cannot be decided after the one 

 known specimen. Only ophicephalous and triphyllous pedicellariæ are found on it, and they show 

 nothing remarkable; the latter are of the same jDeculiar form as in Trigonoc. albida^ biit the edge does 

 not appear to be serrate, even under the highest magnifying powers. The ophicephalous ones are 

 short-necked, and the stalk is constructed as in the other forms mentioned liere. The spicules are 

 bihamate, rather small and numerous (PL VII. Fig. 27). To be sure, this very peculiar Echinid will 

 easily be recognised, even if our knowledge of its pedicellariæ is deficient. 



Tenniechinus maculatus A. Ag. The buccal membrane, as stated by Agassiz, is quite naked 

 with the exception of the buccal piates; but it does not seem to have been observed that it con- 

 tains a great many bihamate spicules. Also the spicules of the tube feet are bihamate. Koehler (229) 

 has described the ophicephalous and globiferous pedicellariæ, not, however, with a sufficiently exact 

 representation of the characteristic structure of the latter. The ophicephalous pedicellariæ are long- 

 necked; Koehler thinks the valves to be uncommonly long, which does not appear to me to be the 

 case; at all events they show no peculiar structure. The globiferous pedicellariæ, on the other hånd, 

 are very peculiar and interesting. The small poison glands are double, and separated 

 through their whole length (PL VIII. Fig. 7), a feature which was hitherto quite unknown in the 

 Echinids, but which I have also found in Parasalenia and iStrongylocoitrotusf crythrogramrmis. 

 Whether this feature is a primitive one, is, I think, to be regarded as doubtful; at all events neither 

 Tetnnechinns^ Parasalenia., nor Strongylocentrofjts can be regarded as primitive forms. In other Echi- 

 nids the poison gland, to be sure, has a deep furrow above on the outside, and opens by a double canal 

 into the end-tooth — at all events xwSphærcchimis (v. Uexkull 406); but this does not appear to me 



