124 



KCHINOIDEA. I. 



plialous pedicellarice 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 triphyllous pedicellarise of the common 

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

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



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

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

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

 pedicellarise 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 pedicellarise 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 Slrongylocen- 

 fr of us-species or with Pseudoccntrotus; on the other hand they seem to be more nearly allied to the 

 genus Loxechinus, a rather great resemblance being found between the globiferous pedicellarise. 

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

 pedicellarise with quite open blade may also sometimes be found (Ech. Alexandri}. Also the triden- 

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

 be a polypore Parechinus, so must also, I suppose, Str. 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. 



Strongylocentrotus tuberculatus (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 pedicellarise. Inside the buccal plates a rather great number of small fenes- 

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

 (PI. XIX. Figs. 4, 13), are constructed as in Echinomelra: 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 pedicellarise 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 pedicellarise show no peculiarities. The stalk of the pedicellarise compact. The spicules 

 bihamate, also those of the globiferous pedicellarise. 



Strongylocentrotus erythrogrammus 1 } and arnnger correspond so exactly with tubcrculatus with 

 regard to pedicellarise 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 pedicellarise in these two species. 



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



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



