16 



areas rather small, Ihe uppermost tubercle of the inner row being found on the 

 fourth plate from above. The triphyllous and claviform pedicellariæ are like those 

 of the other species; the large tridentate pedicellariæ (PI. III. Fig. 20, PI. V. Fig 1) 

 somewhat resemble those of 0. antillarum, mostly having a distinct inward folding 

 in the outer end (this feature may also be found sometimes in antillarum). The 

 small tridentate pedicellariæ (PI. III. Fig. 2) have the outer end of the blade a little 

 broader and the corners towards the side-edge a little farther down than in Ü. antil- 

 larum. The spicules as in D. antillarum. These differences, however, are very slight, 

 and it may be doubtful whether one could say with certainty, if a specimen be 

 Ü. antillarum or mexicanum, if it were not known from which side of America 

 it had come. It can scarcely be doubted that they were one species before the for- 

 mation of the Isthmus. From D. saxatile both are easily distinguished, especially 

 by their pedicellariæ. 



D. Savignyi Mich. The pore areas are not widened at the peristome and 

 the pores are not much smaller below than above the ambitus; there is a primary 

 tubercle to every compound ambulacral plate. Mostly no distinct dark impression 

 on the genital plates. The naked space in the interambulacral areas rather small; 

 the uppermost tubercle of the inner row found on the 5th plate from above. 

 The large tridentate pedicellariæ (PI. III. Fig. 8. PI. V. Fig. 7) — head c. 1,5 mm. — 

 with the blade broad and flat, often somewhat irregular. There may be a pair of 

 wingshaped crests on the back of the blade in the larger ones. In the smaller 

 tridentate pedicellariæ (PI. IV. Fig 37, PI. V. Fig. 9) the blade is broad, with the 

 edge strongly serrate. On the buccal membrane some very small tridentate pedi- 

 cellariæ are found, very similar to those of D. mexicanum (PI. Ill, Fig. 6, PI. V. 

 24). The actinal tubefeet are mostly richly provided with spicules, and often larger 

 irregular fenestrated plates, arranged in three or four longitudinal series, occur in 

 the whole length of the foot; especially at the base of the foot some large plates 

 may be found. In the abactinal tubefeet two longitudinal series of the common 

 triradiate spicules are generally found; they form no supporting beams in the 

 partition wall. 



That this is a distinct species I think is evident from the observations here 

 given. That it is really the D. Sauignyi Mich. I think certain. I have examined in the 

 Museum of Paris a specimen named thus, from Zanzibar, Rousseau 1841. To be sure 

 I found upon it only one large tridentate pedicellaria, which was so crushed 

 that only the basal part was preserved; but in the tubefeet some large fenestrated 

 plates occur, and as I have observed such spicules in no other species, I think we 

 can safely use the name D. Saviyniji for this species. The differences between D. 

 Savignyi and mexicanum are evidently very slight. Upon the whole the three 

 species I). Savignyi, mexicanum and antillarum are very nearly related, where as 

 ]). saxatile stands more distantly, being at once and easily recognized by its narrow 

 tridentate pedicellaria". U. Savignyi probably occurs logelher with D. saxatile in 



