SPATANGIDAE. 197 



to find only 1 tridentate, and that very small, and 2 globiferous. The triden- 

 tate is similar to those of atropos but the valves are only about .18 mm. long. 

 The globiferous are very interesting. The stalk has a remarkable flaring " limb " 

 (PI. 146, fig. 23) with a perfectly smooth edge, quite unlike anything I have ever 

 seen in pedicellarian stalks. The valves are .70-.75 mm. long and resemble 

 those of Schizaster orbignyanus and canaliferus as figured by Mortensen (1907. 

 Ingolf Ech., pt. 2, pi. 14, figs. 2, 8) but there is even less distinction between 

 blade and base, and the apophysis reaches well up above the middle of the valve. 



Moira stygia. 



Moera stygia A. Agassiz, 1872. Bull. M. C. Z., 3, p. 58. 

 Moira stygia A. Agassiz, 1872. Rev. Ech., pt. 1, p. 147. 



This species is recorded from the Red Sea and from Zanzibar. Examina- 

 tion of the only specimen in the M. C. Z. collection, though prolonged, failed 

 to reveal a single pedicellaria. But the specimen is old and dry and has lost 

 many of its spines. 



SPATANGIDAE Gray. 



This is the largest of the families of spatangoids and includes all those 

 forms with more or less developed petals, which also have a subanal fasciole. 

 But in many cases the petals are imperfectly developed and differ little appar- 

 ently from the condition shown by the Palaeopneustidae. In such cases, how- 

 ever, there is reason to believe that the petals were formerly more perfectly 

 petaloid and that the present condition is the result of continued specialization. 

 Yet it must be granted at once that it is highly improbable that the petals of 

 Linopneustes are in any particular essentially different from those of Archaeop- 

 neustes and Palaeopneustes. As for the subanal fasciole it is a well-known fact 

 that in Meoma the subanal fasciole is practically wanting and in certain indi- 

 viduals of Spatangus it may entirely disappear with age. 



The pedicellariae of the Spatangidae are exceedingly varied and there are 

 greater differences between some of the genera within the family than there are 

 between these genera and some of the genera in other families. In many cases 

 ophicephalous pedicellariae are wanting and in others they seem to be present 

 only on young specimens, so we may ultimately find that the presence or absence 

 of ophicephalous pedicellariae will prove a useful character in determining 

 relationships within the family. In certain genera some of the pedicellariae 



