I24 ECHINOIDEA. I. 



phalous pedicellariae have only a strong keel in the middle of the blade, as is seen on the figures of 

 Valentin; otherwise almost no net of meshes is found. The triphyllons pedicellariae of the common 

 form. The spicules bihamate; I have only found them in the buccal tube feet. — Otherwise I may 

 refer to Valentin's excellent figures of pedicellariae and spicules. 



Very closely allied to Sir. lividus is Sir. Gaimardi (Blainv.); it agrees exactly with lividus with 

 regard to pedicellariae and spicules. Unfortunately I have not been able to find tridentate pedicellariae 

 on any of the three specimens found in the museum of Copenhagen, and it is just in the tridentate 

 pedicellariae we might expect to find the difference. I shall express no definite opinion as to the fact, 

 whether it be really the same species as lividus, what Agassiz is inclined to think; at all events the 

 tridentate pedicellariae must be examined, before the question can be answered with certainty. The 

 peculiar, striped apical plates seem, however, to indicate that it is a distinct species. 



It is a sure fact that these two species have nothing to do either with the genuine Strongylocen- 

 trotus-species or with Pseudocentrotus\ on the other hand they seem to be more nearly allied to the 

 genus Loxcchinus , a rather great resemblance being found between the globiferous pedicellariae. 

 These pedicellariae, however, seem to remind more of the genus Echinus itself, where globiferous 

 pedicellariae with quite open blade may also sometimes be found {Ech. Alexandri). Also the triden- 

 tate pedicellariae remind most of the long, narrow form common in Echinus. As Loxcchiuus seems to 

 be a polypore Parcchiuus, so must also, I suppose, Sir. lividus be regarded as a polypore form of 

 Echinus. That it must form a separate genus is not to be doubted. I propose the name of 

 Paracentrotus. 



Strongyloccntrotus tuberculattts (Lamk.). To the description of this species by Agassiz (Rev. 

 of Ech. p. 449) the following informations must be added. A primary tubercle is found on all the 

 ambulacral plates; two ocular plates reach to the periproct. The buccal membrane contains compara- 

 tively few plates, all those outside of the buccal plates, with the exception of the plates at the very 

 edge, are thick and carry pedicellariae. Inside the buccal plates a rather great number of small fenes- 

 trated plates are found. The globiferous pedicellariae have glands on the stalk; no neck; the valves 

 (PI. XIX. Figs. 4, 13), are constructed as in Echinometra: with one unpaired lateral tooth, almost as 

 large as the end-tooth, but, of course, without a poison-canal on the upper side. The blade is tubular, 

 but not quite closed; the basal part is much widened with the fore corners a little produced in a wing- 

 like manner. The tridentate pedicellariae occur in two forms, a more narrow one (PI. XIX. Fig. 8) with 

 only little developed net of meshes, and a broader one (PI. XIX. Fig. 9) with a well developed net of 

 meshes, the meshes of which are somewhat lengthened, especially towards the point of the blade. On 

 the lower part of the edge transverse series of small teeth are found. The ophicephalous and tri- 

 phyllous pedicellariae show no peculiarities. The stalk of the pedicellariae compact. The spicules 

 bihamate, also those of the globiferous pedicellariae. 



Strongyloccntrotus crythrogrannuus 1 ) and armigcr correspond so exactly with tuber culatus with 

 regard to pedicellariae and spicules, that a reliable specific difference is scarcely to be found in these 

 features; I have not, however, seen the broad form of tridentate pedicellariae in these two species. 



That we have here a type which cannot be classed with any of the preceding genera, is 



') Not euryihrogrammus, as it is wrongly spelled in Rev. of Echini. 



