Il8 ECHINOIDEA. II. 



almost straight across tlie anterior ambulacrum from the end of the anterior lateral petals. The latter 

 ara in the northern form about twice and a half as long as the posterior petals; in the sonthern form 

 (to judge from the fig. 2 of Agassiz) they are 4 times as long. It might then well .seem a little 

 doubtful whether they are really the same species — at least they deserve to be carefnlly examined and 

 compared. In case they prove to be different species, the sonthern form nuist keep the name orbigny- 

 amis, as the species was established on specimens from the Caribbean Sea (Prel. Rep. Blake Ech. p. S4). 

 Unfortunately I could not examine this qnestion during my visit to America, as I conld not get 

 access to the Collections of the Mnsenm of Comparative Zoology, and specimens from the Caribbean 

 Sea were not in the Collections of the U. S. National Mnsenm or the Mnseum of Yale College. 



S. orhignyaniis is upon the whole very like canalifcrus ; a carefnl examination, however, shows 

 several more important differences. Agassiz notices as ;;a character which readily distingnishes the 

 specimens of the two species thus far compared* the closer tnbercnlation of orbignyamis. In the speci- 

 mens, I have examined, this is, however, a very little prominent feature; I can indeed scarcely find 

 any difference between the two species in this respect. — Perhaps the statement cited was fonnded 

 on the sonthern form. — In the structnre of the test I find the most important difference between 

 the two species in the arrangement of the pores in the odd anterior ambulacrum. In canalifcrus the 

 pores are arranged in two, close, irregular series, a feature which I find distinct already in a specimen 

 of 23'"™ length ; in orbignyamis these pores form only a single almost regular series (the examined speci- 

 mens ca. 50'""'); the ambulacral piates are thus much higher than in canali/ems. The form of the 

 labrum is a little different, the posterior part being comparatively longer and narrower in orbigvyanus, 

 but as in canalifcrus it does not reach the 2. arabxilacral plate. The' first of the large subanal tubefeet 

 is foimd on the 6th ambulacral plate (on the 5th in canalifcrus); the subanal fasciole passes over the 

 II — i2th plate, as in canalifcrus. Agassiz points out that the latero-anal fasciole varies greatly in 

 distinctness; my observations are in accordance with this; of the two specimens before me one has it 

 very distinct, whereas in the other it is totally wanting. 



The pedicellariæ give ver)' good specific characters. The globiferous pedicellariæ (PI. XIV. 

 Figs. 2, 32) are upon the whole very like those of canalifcrus ; the terminal opening of the valves is 

 surrounded only by a single circle of teeth, 4 (seldom 3) on each side. The second tooth from the 

 point may sometimes be placed a little more laterally from the others. The form of the valves is 

 otherwise like that of canalifcrus. The stalk has at its lower end some free, upwards projecting rods 

 (PI. XIV. Fig. 29); such are not found in canaliferjis. The rostrate pedicellariæ (PI. XIV. Figs. 23, 49) are 

 rather like those of canaliferus; the blade is long and slender, with smooth, somewhat inrolled edges, 

 which may be united by a few crossbeams in the lower part. The point of the blade is rather broad, 

 with about 10 — 16 rather strong teeth. They may reach a length of head of ca. i™™. The neck is 

 very short. Small forms like those of canaliferjis also occur. The tridentate pedicellariæ (PL XIV. 

 Figs. 12, 17) have rather elongate, narrow leafshaped valves, which join in almost their whole length; 

 some of them have a few coarse serrations along the edge in the lower part (PI. XIV. Fig. 17); (up to 

 ca. 07'""' length of head). Only these forms have been found, the tridentate pedicellariæ thus far from 

 reaching the rich development of the tridentate pedicellariæ in canaliferus ; but it may be remarked 

 that I have seen only a few, not very perfectly preserved specimens — a better material will probably 



