ECHINOIDKA. II. rg 



young- stages, I cannot give, since, nnfortnnatcly, no quite small specimens are found among the pres- 

 ent material. On the other hand, I do not doubt, as does Loven (Op. cit. p. 22), that the \oung ones 

 will he found some day. Since we have found (piite \-oung specimens of Hcmiaslir expergitiis (see 

 belowl, a species much more rarely met with than Pourtalcsia Jeffreysi, it seems not improbable that 

 we shall some da\' also have the good fortune to meet with the voiing Pourtalcsia. 



The general form of the test is well described by Loven (Pourtalcsia. p. 6); there is, however, 

 some variation, as pointed out by ^Michailovskij (Echinod. d. Jerniak p. 163). Some specimens 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\' (PI. \'. P'ig. 14), the supra- 

 anal prolongation turning to one side, the anal rostrum to the other. Also the anterior end ma\- be 

 unequally de\-eloped, the one side projecting in front of the other. — The P~igures 19, 21, 23. PI. \' 

 represent a specimen in which the spines are uncommonh' well preserved; the two side-views, PI. V. 

 Figs. 13, 18 show how different the outline in profil ma\' be. (See also M i ch ailo \-sk ij. Loc. cit.) — 

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



Wyv. Thomson states (Op. cit. p. 749) tliat the test is so remarkabh- thin thai 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 deser\es to be noticed that among the Ingolf ; material there 

 are several old tests (St. 113 and 117), which have evident!}- been partl\ or completely embodied in 

 the bottom deposits (they -were fidl of mud); 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 plates are, in 

 the larger specimens at least, generalh- somewhat raised, the plates themselves being somewhat con- 

 cave; this may 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 me to make an addition 

 to our knowledge, whicli is of some importance, \-iz. the labrum and the adjoining ambulacral plates. 

 Lo\-en finds that in P. Jeffreysi 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 plates I.a. i 

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

 and \'. a. 1 are wanting (or, as Loven thinks, coalesced with the large plates I.a. i and V. b. i, which 

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

 examined b\- Loven: P. laguucula. carina fa. and cerafopyga. in which the labrum is distincth- seen 

 from without, separating the inner plates of ambulacra I and \'; the plates I. b. i and V. a. i are al.so 

 developed in these species. 



This feature of P. feffreysi 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 specimens it is seen as a ver\- narrow plate, quite enclosed between the two large 

 inner ambulacral plates, in others it is well developed, reaching to the border of the invagination; it 

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

 (PL VIIL Fig. 10). Regarding the inner plates of ambulacra I and \' there is likewise great variation. 

 I have seen one specimen in which onl\- the plate a. i was developed in ambulacrum I, otherwise I 



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