29 



dorsal rod — ) may be double (Fig. 3 A). The postoral rods are fenestrated, 

 thorny. 



In a plankton sample from ofp the island of Taboga from the end of 

 November 1915 three specimens of an Echinopluteus were found, which 

 may with no small degree of probability be referred to Astropyga pulvi- 

 nata. (PI. V, Fig. 7). The larva shows so considerable resemblance to that 

 figured by Joh. Miiller in his VII. Memoir on the Echinoderm larvae 

 (Taf. V) that it seems beyond doubt they must be nearly related to one 

 another. Joh. Miiller referred his larva to Centrostephanus longispinus. 

 There is still no definite proof that he was right herein, but there is nothing 

 either to disprove the correctness of this reference. The present larva 

 should then also be referred to a Diadematid. Diadema mexicanum being 

 out of question as not having its breeding season at this time of the year, 

 Astropyga pulvinata, the only other Diadematid known to occur here, 

 should then be the species to which this larva belongs. (A new Astropyga 

 found by the author at Las Perlas — not yet described — hardly comes 

 into consideration). It should, however, be pointed out that the postoral 

 and posterodorsal rods are entirely smooth in these larvae, while in the 

 reared young larvse of Astropyga the postoral rods were found to be 

 distinctly thorny. This fact is thus not in favour of the supposition 

 that these larvse belong to Astropyga. Since, however, they must in all 

 probability belong to a form which has a near relative in the Mediterra- 

 nean, there is hardly any other Ethinoid which could come into regard — 

 be it not Eucidaris Thouarsi, which I would not think very probable, 

 judging from the shape of the young larva reared. 



The extensive development of the vibratile lobes, the very long postoral 

 and posterodorsal arms ( — they are broken, so that their full length 

 cannot be ascertained, but they are very long — ), and otherwise the 

 whole shape of the larva is very much like that of the Mediterranean larva, 

 Echinopluteus Mulleri, as I have named it. The posterior transverse rod 

 has a long median process to each side. 



Arbacia stellata (Blv.)i). 



PI. VII, Fig. 3. 



Although a considerable number of young specimens of this species 

 was secured at Taboga, Panama, only a single adult specimen was observed, 



1) H. L. Clark in his paper "Echinoderms from Lower California, with Descriptions of 

 new Species" (Bull. Amer. Mus. Nat. Hist. XXXII. 1913. p. 220) rejects the name Arbacia 

 stellata (Blv.), because of the name Echinus stellatus being used by Gmelin (Linn. Syst. 

 Naturffi. Ed. XIII. 1788. p. 3174), "even though we do not know at present what species 

 Gmelin had in mind"; instead of the long used name A. stellata (Blv.) he then names it 

 Arbacia incisa (A. Ag.) reviving the name given to this species by Agassiz in 1863. I do 

 not ?ee the necessity of making this change, and therefore keep the old name. 



