74 



ECHINOIDEA. I. 



these smaller forms (PI. LXVII. Fig. 7). On PI. XIV. Figs. 8, 17, 18, 24 valves of larger and smaller 

 specimens of this form have been figured; they are all extremely finely serrate in the edge. They 

 are short-necked as the large form, the smallest ones, however, with a somewhat longer neck. The 

 stalk of the common structure. The cover-plate of the triphyllous pedicellarise is highly developed 

 (on PI. XII. Fig. 33 there is a broad, open space in the median line, but most frequently the projections 

 of the edges join in the middle, so that the common series of large holes in the median line is formed); 

 the valves are lengthened, narrow below, rather abruptly widened above. The edge finely serrate. - 

 The sphseridise (PI. XIV. Fig. 14) are somewhat more lengthened than in C. hystrix. 



Wyv. Thomson (op. cit. p. 473) describes the colour of this species very thoroughly. Bell (72. 

 PI. XXIV) gives a couple of excellent coloured figures of the two species hystrix and fenestratum (only 

 the test). As already mentioned he regards them as one species, as he finds very great variation in 

 the size of the uncalcified space between the plates. With regard to the different colouring Bell 

 remarks: The coloration of tests, however, does not often go far in helping in the discrimination of 

 species of Echinoids. He finds a considerable variation in the extent and intensity of the colour, and 

 some specimens are, moreover, quite bleached. -- I am inclined to attach more importance to the 

 colour as a distinguishing mark between the Echinids. To be sure, bleached specimens are often met 

 with, and they, of course, cannot be recognised by the colour, but fortunately specimens are very often 

 found that have kept their natural colour almost completely, and such specimens are found, at all 

 events, in most of the divisions of Echinids. In such specimens the colour is a really good character, 

 as, according to my observations (and I have seen numbers of living Echinids, as well in northern 

 as in tropic seas) the species have most frequently a rather constant and characteristic coloration. 

 However, I think the colour to be only rarely an absolutely reliable character. As to the two 

 figures given by Bell there is, in my opinion, no doubt that Fig. i is A. fenestratum and Fig. 2 

 Calveria hystrix. 



The longitudinal muscles are well developed; I have not been able to find organs of Stewart 

 in the specimen I have opened. 



Only one specimen has been taken by the Ingolf, st. 89 (64 45' N. Lat. 27 20' W. L,. 310 fathoms. 

 Bottom temperature 8), the Denmark Strait. 



With regard to the distribution of this species we have only few sure facts. The Porcupine- 

 Expedition took it off the Portuguese coast; that it is also found off the western coast of Ireland 

 appears with certainty from the paper by Bell (72) quoted above. Agassiz enumerates several 

 localities from the sea round Barbados for A. Reynoldsii, and in British Museum I have myself seen a 

 specimen (called A. hystrix) from Barbados, which is no doubt A. fenestratum. Our museum has 

 further received a specimen from Smithsonian Institution obtained near Florida (32 36' N. Lat. 

 77 29' 15" W. L. 258 fathoms); it is also called A. hystrix, but is A. fenestratum. From these statements 

 it may be concluded with rather great certainty that like Ph. placenta and C. hystrix it is found in 

 the whole northern Atlantic, as well on the American as on the European side, and across the Atlantic 

 south of Iceland on the slopes towards the deep. Its vertical distribution seems to be somewhat 

 smaller than that of the other species, the greatest depth from which it is mentioned, being 373 

 fathoms (A. Reynoldsii, Agassiz, 6); the smallest depth on which it has been taken, is 81 fathoms 



