94 



the well known type characterized by the presence of an unpaired poste- 

 rior process, and as we now know the larvae of the genera Spalanyus, 

 Echinocardium, Aloira, Brissus, Brissopsis and Meoma it is certainly not 

 unreasonable to conclude that this larval type will be found in all those 

 Spatangoids that have typical pelagic larvae. (Brisaster lalifrons and //- 

 gilis most probably have no pelagic larva?, their eggs being large and 

 rich in yolk). It is true, we do not know the larva of any of the Palaeo- 

 pneustida? or of the Meridosternata. But these again would seem to be out 

 of question, because none of these occur in the Gulf of Panama which 

 might account for the two larval species occurring there. 



Then the Cidarida? alone remain. Of these there are, at least, forms 

 enough to account for the different species of the larvae, also those of 

 the Gulf of Panama, although there is only one strictly littoral species 

 there, Eucidaris Thouarsii; but the Cidaris panamensis, with a known 

 bathymetrical range of 66 112 fathoms occurs at the coast of Columbia 

 and might thus far very well come into consideration when looking for 

 the parental origin of the second of the larvae found in the Gulf of Panama. 

 Moreover, the young stage of the larva of Eucidaris Thouarsii described 

 above (p. 22, Pl.V, Fig. 2) really suggests a larval shape like that of Echino- 

 pluleus transversus. There are, however, some great difficulties in refer- 

 ring these larva? to Cidarids. One is that the larva of Cidaris cidaris (Doro- 

 cidaris papillala), reared by Prouho, is of the typical Echinopluteus 

 shape, not in the least recalling the Echinopluteus transversus. It is also, 

 a priori, very improbable that the most primitive of all Echinoids should 

 have one of the most specialized and transformed larval types. And then, 

 of course, the ophicephalous pedicellariae are the chief difficulty. It is, 

 no doubt, possible that such may occur on the newly metamorphosed 

 Cidarid, but are lost very soon. But nobody has found them there as yet. 

 I have examined some young specimens of Eucidaris Thouarsii, only 

 34 mm in diameter, but there was no trace of ophicephalous pedicel- 

 laria? (they should, of course, be looked for on the apical system, as that 

 is their place in the metamorphosing larva); however, there is no definite 

 proof that they may not be found in still younger specimens 1 ). Embry- 

 onic spines of the shape known from other regular Echini, with 3 4 

 points, highly different from the typical secondary spines of Cidarids, 

 were found on the apical system of these specimens. The presence of 

 such embryonic spines, which soon disappear, is certainly in favour of 



L ) In very young specimens from the marsupium of \otocidaris gaussensis there are no 

 ophicephalous pedicellaritf, so that it seems fairly certain that such do not occur in this 

 species at least, which is not in favour of the suggestion that they might possibly occur in 

 other jpecies. 



