84 



ECHINOIDEA. I. 



resemblance in the structure of the test to A.monilis (comp. Chall. Ech. PI. VII. Fig. 15 with PI. XVIII. 

 Fig. 12. a in Desor: ^Synopsis des Echinides fossiles>>, or with PI. XV. Fig. 11 in Agassiz and Desor: 

 ((Catalogue raisonne»), and so I shall establish no new genus for this form, but for the present let it 

 remain in the genus Arbacina. 



Trigonocidaris albida A. Agass. The globiferous pedicellarise (PI. \'II. Fig. 31) chiefly as in 

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

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

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

 The triphyllous pedicellarise are very small and of a rather peculiar form (PI. 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 (PI. VII. Fig. 28), very few. The spines are constructed after the same type as those of Hypsi- 

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



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

 important one seems to be that Prionechimis 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 tliis respect; but I think that the very fact 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 monolini A. Ag. is a real Trigonocidaris cannot be decided after the one 

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

 nothing remarkable; the latter are of the same peculiar form as in Trigonoc. albida, but 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 here. 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 pedicellarise is deficient. 



Temnechinus maculaius A. Ag. The buccal membrane, as stated by Agassiz, is quite naked 

 with tlie exception of tlie buccal plates; but it does not seem to have been ob.served 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 pedicellarise, not, however, with a sufficiently exact 

 representation of the characteristic structure of the latter. The ophicephalous pedicellarise 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 pedicellarise, on the other hand, 

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

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

 Echinids, but which I have also found in Parasalenia and «Strongylocenirottis» erythrogrammus. 

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

 Temnechinus., Parasalenia.^ nor Strongylocentrotus can be regarded as jarimitive form.s. In other Echi- 

 nids the poison gland, to be sure, lias a deep furrow abo\e on the outside, and opens by a double canal 

 into the end-tooth — at all events m Sphcer echinus (v. U ex kill 1 406); but this does not appear to me 



