46 



ECHINOIDEA. II. 



basal part less developed and the blade more rounded than in naresianus; also the arrangement of 

 the teeth along the edge is somewhat different. (PI. IX. Fig. u.) The tridentate pedicellarise (PI. IX. 

 Figs. 25, 27), both larger and smaller forms, are more open than in narcsiamts: (I have seen nothing corre- 

 sponding to the coarse form of tridentate pedicellarise); also the triphyllous pedicellarise (PI. IX. Fig. 12) 

 differ a little from those of the former species, being a little broader. — The miliary spines are like 

 those of naresianus; the primary spines are smooth in the lower part as in that species; if the outer 

 part is also as in naresianus, I cannot say, having seen only broken spines. 



The genus Cystechinus is evidentlv verv nearly related to Urechinus; in fact, I am unable to see 

 how to distinguish these two genera, as hitherto understood. The diagnoses of the two genera in the 



Challenger; -Report (p. 146, 148) do not preciselv indicate the differences; the only distinguishing character 

 which may be gathered from these descriptions of the genera is sthe rudimentary auricles, the raised 

 edge of the actinal opening mentioned for Cystechinus. This feature, highly interesting indeed and 

 important from a morphological point of view, as pointed out by Agassiz, is, however, found fully 

 as distinctly developed in Urechinus narcsiamts (Fig. 3). This character cannot thus be used for dis- 

 tinguishing the two genera. I am likewise unable to find in the elaborate diagnoses of the genera 

 given by Duncan (Revision p. 212 — 13) and by Gregory 1 an} - distinguishing feature of reasonable 

 importance. In all the more important features the}' agree: structure of ambulacra and interambulacra, 

 sternum, actinal and apical system, tube-feet, spines and general shape of the test. The only characters 

 I can find, which might be taken into consideration for distinguishing them as different genera are 

 the following: a subanal fasciole is generally found in young specimens of U. naresianus, whereas it 

 is not found in Cystechinus; but in larger specimens of U. naresianus the fasciole has generally dis- 

 appeared, even so fully that Loven could find in the structure of the test a sure sign of the total 

 absence of the fasciole, and in U. giganteus it is not found either. On the other hand it seems to be 

 found in Cystecii. clypeatus, since according to Agassiz (Challenger -Ech. p. 149) the edge of the 

 test adjoining the anal system is thickly covered by miliaries forming a broad band, with an indistinct 

 outer edge (almost a fasciole) surrounding it . — The position of the periproct is below the ambitus 

 in Cystechinus (unknown in C. clypeatus); in U. naresianus it is generally not quite below the ambitus, 

 but the difference is, indeed, very slight, and in U. giganteus it seems to be quite as in Cystechinus. 

 Finally I may notice the difference in the structure of the pedicellarise, especially the globiferous — 

 but if the genera were to be founded upon the structure of the globiferous pedicellarise, we would 

 have to make U. naresianus the type of one genus, to unite U. giganteus, Cystech. Wyvillii and Lovcui 

 in another genus, further to make a separate genus of UrecJi. Drygalskyi 2 and a fourth genus of 

 C. clypeatus. I think Professor Agassiz would be the first to object against founding these genera 

 on the differences in the globiferous pedicellarise alone, and I for ray part do not hold that necessary' 

 either. But then the conclusion is inevitable that the genera Urechinus and Cystechinus cannot be 

 distinguished as hitherto understood. Cystechinus then becomes a synonym of Urechinus. or in any 

 case the species C. Wyvillii and Loveni must be transferred to Urechinus. Probably the C. clypeatus 

 (or one of the species confounded under that name) will prove to make a separate genus, which will 



then keep the name Cystechinus. The Cystech. vesica has recently been removed by Agassiz himself 



1 Cystechinus crassus, a new Species from the Radiolarian Marls at Barbados. Quarterly Jouni. Geol. Soc. 1S89. p. 640. 



2 Th. Mortensen: Some new species of Echinoidea. Vidensk. Medd. Naturh. Foren. Kobenhavn. 1905. p. 241. 



