ECIllNOTHURID^. 145 



66, fig. 20) and may even be greatly reduced, with the expanded tip entirely 

 lacking; this form, which occurs in A. pellueidum, was at first regarded hy 

 Mortensen as a " globiferous" pedicellaria; but he was subsequently satisfied 

 by de Meijere's evidence, that it is simply a degradational form of dacty- 

 lous pedicellaria. There are no globiferous pedicellariae known in the 

 Echinothuridas. 



As Doderlein has well pointed out, the three families Aspidodiadematidoe, 

 Diadematidae, and Echinothuridas show such agreement in the essential 

 features of their pedicellarifle that they form a group apart from the other 

 regular Echini, and arouse the suspicion that they are mutually interrelated. 

 In the absence of globiferous pedicellariae (present only in Centrostephanus) 

 they agree with the Salenidae and Arbaciadae, and differ markedly from the 

 Cidaridae, Echinometridce, and Echinidae. Their mutual agreement in triden- 

 tate pedicellariae is obvious, but in view of the great diversity of form which 

 these pedicellariaB show in the three families, and of the fact that very 

 similar pedicellariae occur in other families, no great weight can be laid on 



this point. The ophicephalous pedicellariae of the Echinothuridae are pe- 

 culiar but are as much like those of the Diadematidae as of any other echini, 

 excepting only some of the spatangoids. The triphyllous are similar to those 

 of the Aspidodiadematidae ; they are less like those of Astropyga and Micro- 

 pyga, but still the resemblance even here is not to be ignored. 



The sphwridia of the Echinothuridse (Pis. 66, figs. 4, 6, 18 ; 67, fig. ll), as 

 in the Aspidodiadematidae and many Diadematidae, are more or less numerous 

 in each ambulacrum and occur at the inner lower side of the tube-feet in the 

 innermost series. In Phormosoma they are also present next to the feet of 

 the middle series. They may be confined to the actinal surface of the test, 

 but commonly they extend above the ambitus. They sometimes accompany 

 the tube-feet nearly or quite to the ocular plate, and occasionally they may 

 be found on the buccal plates. In Phormosoma they are nearly spherical, 

 but in the other genera they are more or less elongated ; sometimes the 

 length and appearance (PI. 66, fig. 18) indicate clearly their origin as modi- 

 fied spines. 



The calcareous spicules of the tube-feet are commonly in the form of perfo- 

 rated plates (PI. 65, figs. i4, 20), which show great diversity in form and 

 size. In some species, however, the spicules, either in the basal part of the 

 foot or throughout its length, are simply more or less irregular triradiate 

 rods (PL 66, fig. 13), similar to those found in the Diadematidae. There 



10 



