ECHINOIDEA. l 



85 



a sufficient proof of the original structure having been a double poison gland. We should then except 

 to find a double poison gland in forms as Hypsiechinus and Parechinus] in these, however, it is not 

 found - - but on the contrary in such specialised forms as the three species mentioned above. More 

 thorough examinations will be necessary in order to decide the question. The histological examina- 

 tions hitherto made of the globiferous pedicellaria; , have chiefly been directed to Sphcsrechinus ami 

 Echinus acutus\ a much broader base of the examinations is necessary. — The form of the valves is 

 rather peculiar; the basal part is flatly widened, with rather sharp corners, the blade very narrow, 

 almost tubiform, the edges being almost quite coalesced on the inside, so that only a series of small 

 holes are found along the median line and one larger hole at the point; only one unpaired lateral 

 tooth (PI. VII. Fig. 30). The triphyllous pedicellariae (PL VII. Fig. 24) are very small and resemble those 

 of Trigouocidaris; no teeth are found in the edge. 



Agassiz originally described this species nnder the name of Genocidaris maculata, later he 

 thought that it ought to be referred to the genus Temnechinus, established by Forbes 1 ) for some 

 fossil forms with rather deep grooves in the sutures. The present species, however, has no such 

 grooves; Agassiz also admits that it shows «very marked differences from the species of Temnechinus 

 figured by Forbes» (Rev. of Ech. p. 286). But when the structure of the test is not the same in the 

 fossil species and the recent one, we cannot be warranted in classing them together; even if the struc- 

 ture of the tests was identical, we might doubt whether they were the same species, for, as has con- 

 stantlv been shown by these examinations, identical structure of the test is no proof of near relation- 

 ship. But when the structure of the test is so different, as the case is here, there can be no question 

 of classing them together. Nor does it show any nearer relation to Opeckinus Desor, to which genus 

 it, according to Agassiz (Rev. of Ech. p. 286), is .closely allied.; Opechinus is a genuine Temno- 

 pleurid with deep grooves in the sutures. I must completely assent to the opinion of Pom el that 

 this form ought to keep its original name of Genocidaris maculata. 



This little Echinid, which was hitherto only known from the American side of the Atlantic 

 and the Azores, is also found in the Mediterranean. In our museum four specimens of it are found 

 taken at Syracuse on a depth of 12—15 fathoms by Dr. H. I. Hansen in 1893. Another species, 

 Temnechinus* Scillcs, from the Red Sea, has been described by Mazzetti (277—78). 



By the name of Arbaciua Pallaryi Gauthier (162) has described a little Echinid from the 

 coasts of Algeria, but it cannot be seen from the description and the figures where this form is to be 

 referred. Prof. Pallary has most kindly sent me some specimens of it, among others three which 

 have been determined by Gauthier himself as A. Pallaryi. They proved to be Genocidaris maculata; 

 thus the name of Arbacina Pallaryi may be struck out as a synonym. That it has no relation to the 

 genus Arbaciua is sufficients evident from the fact that in Arbacina the base of the tubercle is 

 smooth, as is expressly stated by Agassiz, Desor, and Pom el, and shown in the figures of A. man His 

 quoted above. But it is quite incredible that a form with a stellate tubercle-base should be of the 

 same genus as the mentioned Arbacina with smooth tubercle-base. 



It seems to be unquestionable that Hypsiechinus is most nearly related to the forms here men- 

 tioned; its spines, buccal membrane, and structure of the test reminds very much of those, especially 



M Monograph of the Echinodermata of the British Tertiaries. 1S52. 



