124 



ECHINOIDEA. I. 



phalons pedicellarice hav'e only a strong- keel in the middle of the blade, as is seen on the fignres of 

 Valentin; otherwise almost no net of meshes is fonnd. The triphyllous pedicellarite of the common 

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

 refer to \'alen tin's excellent figures of pedicellariae and spicules. 



\'er\- closely allied to Sfr. lividus is Str. Gaiiiiardi (Blainv.); it agrees exactly with lividiis with 

 regard to pedicellariae and spicules. Unfortunately I ha\e not been able to find tridentate pedicellarise 

 on au}- 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 tlie fact, 

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

 tridentate pedicellarise nuist 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 Slroiigyloccn- 

 /w/'/cj-species or with Psc2tdocrntrotHs\ on the other hand they seem to be more nearly allied to the 

 genus Loxfc/iiiiKs, a rather great resemblance being found between the globiferous pedicellariae. 

 These pedicellaricC, however, seem to remind more of the genus Ecliiiuts itself, where globiferous 

 pedicellariae with quite ojjen blade may also sometimes be found [Ecli. ^\.lcxa)idri). Also the triden- 

 tate pedicellarite remind most of the long, narrow form connnon in Ecltimts. As Loxechinus seems to 

 be a polypore Parrc/iiiius\ so must also, I suppose, Sir.y livid/ts be regarded as a polypore form of 

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

 Paracentrotus. 



Strongylocentrotus tiibcrcttlatiis (Lamk.). To the description of this species by Agassiz (Rev. 

 of Ecli. 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 Ec/ii//oi//c/r(i: 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 numner. The tridentate pedicellaria: occur in two forms, a more narrow one (PI. XIX. P"ig. 8) with 

 only little developed net of meshe.s, and a broader one (PI. XIX. Fig. 9) with a well de\-eloped net of 

 meshes, the meshes of whicli 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- 

 Ijhyllous pedicellariae show no jjeculiaritics. The stalk of the pedicellariae compact. The spicules 

 bihamate, also those of the globiferous pedicellariae. 



Stroiigylociii/ro/iis crytlirograiiuniis^) and aniiigcr correspond so exactl\- with titbrrculatiis with 

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

 features; I ha\-e not, howe\'cr, seen the brcxul form of tridentate pedicellari;e in these two species. 



That we have here a type which cannot be classed with an\' of tlie preceding genera, is 



') Not eurytlirogranimus, as it is wrongly spuUecl in Rev. of I-kiiini. 



