46 



ECHINOIDEA. II. 



basal part less developed and the blade more rounded tlian in narcsianus; also the arrang-ement of 

 the teeth along the edge is somewhat different. (PI. IX. Fig. ii.) The tridentate pedicellariæ (PI. IX. 

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

 spondingto the coarse form of tridentate pedicellariæ); also the triphyllons pedicellariæ (PI. IX. Fig. 12) 

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

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

 part is also as in narcsianus. I cannot sav, having seen onl\' broken spines. 



The genus Cystec/iiinis is evidently ver\- nearly related to Urecliiiius; in faet, I am nnabie to see 

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

 Challen ger »-Report (p. 146, 148) do not precisely indicate the differences: the only distinguishing character 

 which ma\- be gathered from these descriptions of the genera is *the rndimentary anricles, the raised 

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

 important from a morphological point of view, as pointed out b\- Agassiz, is, however, found fulh- 

 as distinctly developed in Urrc/iiiiiis itaresianits (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 bv Duncan (Revision p. 212— 13) and by Gregory' any distinguishing feature of reasonable 

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

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

 I eau 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 C naresiamis. whereas it 

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

 appeared, even so full>- that Loven could find in the strticture of the test a sure sign of the total 

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

 found in Cystcch. clypeatns. since according to Agassiz (<Challenger -Ech. p. 149) tthe 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. iiaresiatnis it is generalh' not quite below the ambitus, 

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

 Finally I may notice the difference in the structure of the pedicellariæ, esjjecially the globiferous — 

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

 have to make U. narcsianus the type of one genus, to unite U. gigantens. Cystcch. Wyvillii and Lovcni 

 in another genus, f urther to make a separate genus of Ur ech. Drygalskyi^ and a fourth genus of 

 C. clypeatus. I thiuk Professor Agassiz would be the first to object against fouuding these genera 

 on the differences in the globiferous pedicellariæ alone, and I for m\- part do not hold that necessar)- 

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

 distinguished as hitherto understood. Cystechinus then becomes a syupn^m of Urechinus, or in any 

 case the species C. Wyvillii and Loveni must be transferred to Urechimis. Probably the C. clypeattis 

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

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



' Cystechinus crassus, a new Species from the Radiolarian Maris at Barbados. Ouarterlj- Journ. Geol. ,Soc. 1S89. p. 640. 

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



