KCHINOIDEA. II. 8l 



disconnected like that of 1\ hii^iiiiaila. It is t)eyond doubt tliat in a restriction of the .t,rL-nns the name 

 Pourtalrsia lias to be retained lor the "ronj) of species to which /'. iiiiranda belongs. Thus far I agree 

 with Aoassiz, whose above cited proposition of a subdivision of the genus is evidently much more 

 in accordance with the natural relations of the .species than Duncan's and l't)niers snbdivi.sions. 

 Nevertheless I cainiot fullv accept .\gassiz' subdivisions either. 



On reviewing the characters of the species it .seems to me that one feature may rea.sonably be 

 taken to be of primary importance for a grouping of the species, viz. whether the bivial ambulacra are 

 interrupted !)y the postero-lateral interambulacra or not. Also the shape of the test seems rather im- 

 portant, whereas pedicellariae and spines seem to be of secondary importance. The character of the 

 apical system, whether it is disconnected or compact, cannot be used, all the species thus far known 

 ha\'ing in fact a disconnected apical s\'stem '. 



The bivial ambulacra are continuous in Cdrimita (almost certain!), phialc, paradox^ and pro- 

 bably crratopyga, disconnected in the other species (I', rosra, Jiispida and mirafida are unknown in this 

 respect, but the two latter ma>' well be supposed to have them disconnected). Further it is to be re- 

 marked that J', carmata differs from all the other species in having two pores and tube-feet in the 

 ambulacral plates I. a. i and V. b. i. [P. rosra and ininuida again are unknown in this respect, though 

 the latter may doubtless be supposed to ha\^e the pores single as in lagniiciila etc.). Finally it ma>' 

 perhaps be a character of some importance whether the dorsal plates of the odd posterior interambu- 

 lacrum are paired or alternating, the latter being, of course the more primitive structure; tlie\- are 

 alternating in P. caritiata and ccrafopygn. paired in Jcffrcysi, Wandcli, Iiispida , lagnncula, Tanneri, 

 phialf and parndoxa. Upon the whole this character evidently cannot, however, be taken too rigorously, 

 the paired plates generally showing more or less distinct traces of their originally alternating condition. 

 In typical examples the difference between these structures is verv conspicuous, as seen e. g. b\' a 

 comparison of Figs. 51 and 32. PI. VII in Loven's: On Pourtalesia. In accordance with the characters 

 pointed out here as the more important, I think the following grouping of the species will prove to 

 be the natural one: 



1. Bivial ambulacra continuous; two pores in the ambulacral plates I. a. i and 

 V. b. I. Test not especially widened or elongate. Dorsal plates of odd 

 interambulacrum alternating P\ cnruiata. 



2. Bivial ambulacra continuous; one pore in the plates La. i and \'. b. i. Test 



very elongate ; dorsal plates of odd interambulacrum paired I\ pliiulr and paradoxa. 



3. Bivial ambulacra (probably) continuous; one pore (sometimes two) in the 

 plates I. a. i and V. b. i. Dorsal plates of odd interambulacrum alternating. 



Test much widened anteriorly /-*. ccratopyga. 



4. Bivial ambulacra disconnected; one pore in the plates I. a. i and \'. b. i. 

 Dorsal plates of odd interambulacrum paired. Test not especially widened 



or elongated P. lagnncula, juiraiida (?), 



Unknown : P. rosea. Tannrn'. Jcff'nysi. Wajidcli and Iiispida. 



■ Whether the genital plates be separate or not, .seems to be .1 character of small importance, .since both cases may 

 occnr in the same species. Likewise the presence or absence of the labrum is of small importance, as shown by its great 

 variation in P. Jeffrey.<ii and Jl 'nndc/i. 



The Ingolf-Expeiiition. IV. 2. II 



