22 ECHINOIDEA. I. 



are two forms, a larger and a smaller, both three-valved. In the larger form the blade is filled by an 

 exceedingly rich net of meshes, in which the holes are rather distinctly arranged serially, and radiate 

 in a fanshaped way from the npper end of the apophysis; this net is covered with numerous small 

 thorns, especially towards the point. Also the npper edge of the apophysis is very broad and fnll of 

 holes. (The figures in the Challenger»-Echinoids, PI. XLIV, 6—14, are not very good, especially not 

 figs. 6 and 11, where it is not seen at all that the whole mass filling the blade, is really a net of 

 meshes with innnmerable larger and smaller holes). In the other, smaller form the apophysis has the 

 common structnre; the blade is highly compressed, deep, and filled with an irregnlar net of meshes 

 where the holes are not at all serially arranged. Transitions are however fonnd between the two 

 forms, so that they cannot be said to be two distinct kinds. When Agassiz (Chall. Ech. p. 43) says 

 of the large-headed, shortstemmed pedicellariæ» that they are <,very similar to those oi Dorocidaris'., 

 this is only so far correct, as tridentate pedicellariæ, of conrse, always in some degree resemble each 

 other; in the finer structure the large tridentate pedicellariæ of this species are especially widely 

 different from those oiD.papillata. The small ones are much more similar. — Agassiz (1. c.) mentions 

 one more form of pedicellariæ, shortstemmed globnlar abactinal pedicellariæ > (PI. XLIV, 10); they are, 

 as I have been able to substantiate, only developmental forms of the large tridentate pedicellariæ. I 

 am a little in doubt whether globiferoiis pedicellariæ are fonnd. In my preparation of isolated skeleton- 

 pieces of pedicellariæ of this species is seen one valve of a small globiferous pedicellaria, which is very 

 peculiar, with two large teeth at the point, and a rather small opening surrounded by well developed 

 teeth (PI. IX, Fig. 2). As, however, only one snch valve is fonnd, it may be thonght to have come in 

 b)- chance; in this case it must be abnormal, as no other Cidarid examined by me, is possessed of 

 snch pedicellariæ. For the present this innst be left nndecided. — It is obvions that this species has 

 no relation with P.piirptirata, and as it shows no nearer relation to any other known species, it mnst 

 form a separate genus, for which I propose the name of Histocidaris. 



P. Sharrcri: Agassiz (9) unfortunately gives no details as to the pedicellariæ, and from the 

 figure (op. cit. PI. III) it cannot be decided whether it is a genuine Porocidaris. There seems to be no 

 highly developed neck on the spines (in the text nothing is said of this feature); the pedicellariæ 

 might well look like those of P. purpurata^ but a close examination will be necessary for the decision. 

 By the kindness of Prof. Rathbun I have from U.S. National Museum received a specimen deter- 

 mined && P. S/iarreri (<:Albatross» 1885. St. 2415); it jjroved to be the new species Stcreocidaris ingolfiana 

 described hereafter; it has no relation to P. Sharrcri. Further I have in British Museum seen a 

 specimen determined as P. Sharrcri^ from U. S. Fish Commission ( Albatross^ 1885. St. 2345). Neither 

 seems this specimen to be identical with the real, figured P. Skarrer^ at all events it does not to any 

 striking degree resemble the figure given by Agassiz. It is no Porocidaris. The pedicellariæ (PI. IX, 

 Fig. 26) are much like those of Dorocidaris , only the opening of the large globiferous pedicellariæ is 

 more round and of a more definite form than is otherwise the case in this genus; but this faet might 

 very well be interpreted as a specific difference. Tridentate pedicellariæ simple. A much more con- 

 siderable difference is found in the spines; they are long, slender — unfortunately they were broken, 

 so that their length and the form of their point are unknown. The base is finely pink, the outer 

 part white. They are quite smooth and shining, as if polished, and the structure of the outer layer 



