ECHINOIDEA. II. 59 



voung stages, I camiot give, since, unfortunately, 110 qnite small speciniens are found aniong tlie pres- 

 ent inaterial. On the other band, I do not doubt, as does Loven (Up. cit. p. 22), that tlie young ones 

 will be fonnd some daw Since \ve have found quite \oung speciniens of Hcmiastcr expergitus (see 

 below), a species mnch more rareh" met with than Pourtahsia Jeffrcysi, it seems not improbable that 

 \ve shall some da\- also have the good fortune to meet with the young Ponrtalcsia. 



The general form of the test is well described by Loven (Pourtalesia. p. 6]; there i.s, however, 

 some variation, as pointed out by iMichailo vskij (Echinod. d. ..Jermak- p. 163). Some speciniens are 

 rather short and broad and with short anal rostrum, others are rather flattened; also deformities occur 

 not very seldom, with irregular depressions or with the posterior end awr}- (PL V. Fig. 14), the supra- 

 anal prolongation turning to one side, the anal rostrum to the other. Also the anterior end may be 

 unequally developed, the one side projecting in front of the other. — The Figures 19, 21, 23. PI. V 

 represent a specimen in whicli the spines are uncommonly well preserved; the two side-views, PI. V. 

 Figs. 13, icS .show how different the outHne in profil may be. (See also Michailo vskij. Loc. cit.) — 

 The species reaches a considerable size; the largest speciniens at hånd are up to 58™'" in length. 



Wyv. Thomson states (Op. cit. p. 749) that the test is so remarkably thin that it will scarcely 

 bear its own weight . I do not find the test of this species so very fragile; on the contrary, I find it 

 almost stout for a deep-sea species. It deserves to be noticed that aniong the Ingolf material there 

 are several old tests (St. 113 and 117), which have evidently been partly or coinpleteh' embodied in 

 the bottom deposits (they were full of niud|; most of them are quite uninjured. On one of these tests 

 was found a sea-anemone, on another a sponge. — The sutures of the abactinal lateral piates are, in 

 the larger speciniens at least, generally somewhat raised, the piates themselves being .somewhat con- 

 cave; this ma\- perhaps be a structure tending to strengthen the test. 



The morphological structure of the test has been most admirably worked out by Loven. 

 There is, however, one point of interest on which m\- rich material enables nie to make an addition 

 to our knowledge, which is of some importance, viz. the labrum and the adjoining ambulacral piates. 

 Loven finds that in P. Jeffrcysi the labrum is quite rudimentary, only represented by a small plate 

 on the incurved edge, below the actinostome and not seen from without. The ambulacral piates I. a. i 

 and \'. b. i are large and join in the median line in their whole length, whereas the piates I. b. i 

 and V. a. 1 are wanting (or, as Loven think.s, coalesced with the large piates La. i and V. b. i, which 

 are thus really compound; p. 83) — a considerable difference between this species and the other species 

 examined b>- Loven: P. laguncula. carinata and cerafopxga, in which the labrum is distinctly seen 

 from without, separating the inner piates of ambulacra I and \'; the piates I. b. i and V. a. i are also 

 developed in these species. 



This feature of P.Jefreysi is, however, no constant one. To be sure, the labrum is often, per- 

 haps in most cases, not to be seen from without; but there is considerable variation with regard to 

 this plate. In some speciniens it is seen as a ver>- narrow plate, quite enclosed between the two large 

 inner ambulacral piates, in others it is well developed, reaching to the border of the invaginatiou ; it 

 may even be divided into a larger outer part and a smaller inner part at the edge of the invagination 

 (PI. VIII. Fig. 10). Regarding the inner piates of ambulacra I and V there is likewise great variation. 

 I have seen one specimen in which only the plate a. i was developed in ambukicrum I, otherwise I 



