r.EPORT ON THE ECHINOIDEA. 183 



and it is only later that the differences in the depth and width of the petals becomes 

 apparent, as I have shown in the figures of Hemiaster on plate iv. of the " Hassler " Echini.^ 

 " The figures given on plate iv. figs. 4-8, are aU natural size, and show the changes the 

 lateral ambulacra undergo as they pass from fig. 8 to fig. 7, and from fig. 6 to fig. 4. 

 When the specimens reach the size of fig. 7, the change from comparatively shallow 

 lateral ambulacra to the deep ambulacra of fig. 6 takes place without a great increase in 

 the size of the test. The anterior ambulacra, eventually the most concave (fig. 4), are the 

 first to show marked signs of depressions, and in slightly older specimens than figs. 7 or 

 6 they are already deeply sunken, while the posterior lateral ambulacra are comparatively 

 shallow. In most of the specimens examined I have found large globular, short-stemmed 

 pediceUariae situated in the sunken ambulacral petals, usually the anterior pair, as 

 mentioned by Phdippi. Owing to the comparatively long spines of the edge of the petals, 

 the sunken ambulacra are completely hidden by a screen of spines. The changes of out- 

 line of the test are very limited after the specimens have attained the size figured on 

 plate iv. fig. 8. The outline of the test is somewhat more angular and gibbous, seen from 

 above, and perhaps less conical and somewhat more flattened at the apical system. The 

 number of genital pores is variable, as we find two or three quite indifierently ; the 

 posterior pair of genital openings is always present, if a third exists it is the right anterior 

 one usually, but sometimes the left. In the youngest specimen figured the outline of the 

 peripetalous fascicle is nearly the same as in the oldest specimen examined (fig. 4), though 

 its breadth becomes greater with advancing age. The odd anterior ambulacrum increases 

 but little in dej)th and breath with increasing size." 



In the magnified views of the apical system of a male (PI. XX." fig. 21) and of a 

 female (PL XX." fig. 22), the difference between the size of the genital openings is very 

 striking, as well as the sudden sinking of the floor of the apical extremity of the paired 

 ambulacra in the female to form the marsupial pouches. The genital openings are 

 developed comparatively late, there is no trace of them until they attain the size figured 

 on Plate XX.'' fig. 15. In one female (PI. XX.* fig. 19) there were only two genital open- 

 ings, and it was the left anterior which disappeared next, leaving the two posterior genital 

 openings. 



Professor A. E. Verrill has carefully described the differences existing between the 

 males and females of specimens collected at Kerguelen Island by Dr J. H. Kidder 

 (BuU. U. S. Nat. Museum, No. 3). These specimens he described under the name of 

 Bemiaster cordatus (Bull. U. S. Nat. Mus., 1876, No. 3, p. G9), as he, not having a 

 sufficient series of the South American species [Hemiaster cavernostis and Hemiaster 

 australis) for comparison, preferred to regard it for the present as distinct. The specimens 

 he sent me at the time for comparison 1 could not distinguish from the South American 

 species. The Challenger series is so extensive, and shows such a range of variation 



' A. Agassiz, 1874, Zool. Results of the " Hassler " Expedition, 111. Cat. Mus. Comp. Zool., No. 8. 



