36 



any reliable dilTerence between Ihe Allanlic and tlie Pacific specimens, so il seems 

 really lo be Irne that this species has so wide a distribution. 



Aspidodiadema Jacohyi. The s|)icules are as in A. tonsiim ; in the upper part 

 of the lubefeel, however, they take the I'orm of larger, irregular, fenestrated plates; 

 they are arranged in two longitudinal series. Of the pedicellariæ only one form, 

 the „sheathed" ophicephalous („clavilbrm") ones have been mentioned and ligured 

 by Agassiz; as in A. tonsiim tridentate, triphyllous and ophicephalous pedicellariæ 

 are found. The tridentate pedicellariæ (PI. V. Fig. 28) are rather small, c. 1 mm. 

 (head); the valves are simply leafshapcd, without meshwork in the bottom; they 

 join in almost their whole length. The neck is short. The oj)hicephalous pedicel- 

 lariæ occur in two forms, a large form without glands on the stalk and a small- 

 headed form with large glands on the stalk (claviform), both with the head ])laced 

 directly on the stalk , as in all the Aspidodiademalidiv. The valves in the large 

 form (head c. 1'5 mm.) are elongated, with a coarse meshwork lilling the blade 

 (PI. III. Fig. 25); the edge is thick, smooth and sinuate, the point forming a more or 

 less distinct hook. The second form is provided with very large stalkglands (I have 

 not found this form without glands ), as is well seen in the figures given by 

 Agassiz („BIake"-Echin. PI. IX. a. fig. 9); the head is very small, with slightly deve- 

 loped valves, which present, however, an undoubted ophicephalous structure (PI. IV. 

 Fig. 10). The triphyllous pedicellariæ (PI. IV. Fig. 20) essentially as in A.tonsum; 

 the upper edge of the coverplate is a little produced over the blade, which may, 

 however, also be the case in A. tonsum. The stalk of the pedicellariæ is irregularly 

 fenestrate, but not articulate, as said by Agassiz (for the claviform pedicellariæ); in 

 the claviform pedicellariæ the upper end of the stalk is cupshaped. — There are 

 distinct genital papillæ. 



Aspidodiadema nicobariciiin Doderl. has been treated by de Meijere (Op. cit. 

 p. 4(5), to whose work I may refer. I may only add that I have found two sorts of 

 tridentate ]iedicellariæ on a specimen, which Prof. Döderlein very liberally allowed 

 me to examine; the one form is like that of A. tonsum, the other, much larger form, 

 like that figured in PI. III. Fig. 28 and PI. V. Fig. 80 of A. microtuberciilatiim. The 

 ophicephalous pedicellariæ (only claviform ones observed) seem to be constantly 

 four-valved. 



Aspidodiadema microtiihercalaliim Ag. Under this name Agassiz has con- 

 founded two species; since I have examined the „Challenger"-specimens in the British 

 Museum, I can state this with certainty. The specimen from St. 134, off Tristan 

 d'Acunha, accords well with the description and may thus be taken as the type of the 

 species microtuberciilatiim. It has as yet retained the dark violet colour. There 

 are spines on the buccal plates, a feature not mentioned by Agassiz; the figures, 

 however, show several tubercles on Ihe buccal plates, and the expression „when 

 denuded" used of them in the text may indicate the same thing. It must further be 

 emphasized that the ambulacral plates have not all an equally large tubercle in 



