124 



ECHINOIDEA. I. 



phalons pedicellariæ have only a strong keel iii the iniddle of the blade, as is seen on tlie figures of 

 Valentin; otherwise almost no net of meshes is foiind. The triphyllous pedicellariæ of the common 

 form. The spicules bihamate; I ha\-e only fonnd thern in the bnccal tnbe feet. — Otherwise I mav 

 refer to Val en tin' s excellent figures of pedicellariæ and spicules. 



\'erv closeh- allied to Sfr. liv/dus is Sfr. Gai)uardi (Blainv.); it agrees exactly with lividus witli 

 regard to pedicellariæ and spicules. Unfortunateh I ha\e not been able to find tridentate pedicellariæ 

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

 pedicellariæ \ve might expect to find the difference. I shall express no definite opinion as to the faet, 

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

 tridentate pedicellariæ must be examined, before the question can be answered with certaintv. The 

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



It is a sure faet that these two species have nothing to do either with tlie genuine Stroigyloccn- 

 //-i^^/j-species or with Psriidocciifrotiis\ on the other hånd they seem to be more nearly allied to the 

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

 These pedicellariæ, however, seem to remind more of the genus Echinus itseif, where globiferous 

 pedicellariæ with quite open blade may also sometimes be fotmd [Ech. Alexaiidri). Also the triden- 

 tate pedicellariæ remind most of the long, narrow form common in EcJiimis. As Loxccliimis seems to 

 be a polypore Parccltiinis, so must also, I suppose, .Str. lividus be regarded as a polypore form of 

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

 Paracentrotus. 



Strongyloccntroitis tiibcrailatus (Lamk.). To the description of this species b>- Agassiz (Rev. 

 of Ech. p. 449) the following informations must l)e added. A primår}- tubercle is found on all the 

 ambulacral piates; two ocular piates reach to tlie periproct. The buccal membrane contains compara- 

 tively few piates, all those outside of the buccal piates, with the exception of the piates at the verv 

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

 trated piates are found. The globiferous pedicellariæ have glands on the stalk; no neck; the valves 

 (PI. XIX. Figs. 4, 13), are constructed as in Echinouiclra: 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 pedicellariæ occur in two form.s, 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 de\-eloped net of 

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

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

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

 bihamate, also those of the globiferous pedicellariæ. 



Slrougylocc II trotus crythrograiiiiims^) and arviiger correspond so exactly with fubcrculatios \\\W\ 

 regard to pedicellariæ and spicules, that a reliable specific difference is scarceh' to be found in these 

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



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



') Not eui-yi/irogram»ms, as it is wrongly spelled in Rev. of Echiiii. 



