298 Transactions of the Society. 



found that every genus of the so-called Triplechinidse which I 

 examined contained these same bodies ; similarly they were to be 

 found in the other division (Temnopleuridae) of the Echiuidae, as 

 limited by Professor Alexander Agassiz. Nor were they here only ; 

 when the suckers of the Echinometridae were examined, the biha- 

 mate spicules were again to be observed. In the Cidaridae, 

 SalenidsD, Echinothuridse, Echinocidaridae, and Diadematidae, the 

 bihamate spicules were, on the other hand, conspicuous by their 

 absence ; and this being so, I found in their distribution among 

 various genera of the Echinometridae and Echinidae a gratifying 

 support to the view on which I have elsewhere t insisted, that 

 these two groups differ less from one another than they do from 

 any other group of the regular Echinoids. It may be worth while 

 to give the names of the genera examined : — Heterocentrotus, Colo- 

 hocentrotus, Ecliinometra, EcMnostrejihus* Strongylocentrotus, 

 Splicer echinus* Pseudoholetia* Temnoiileurus, Salmacis, Mes- 

 jpilia, AmUypieustes* MicrocypJms* Cottaldia* Echinus, Trip- 

 neustes, Toxopneustes* Evecliinus* 



The number of genera examined is now sufficiently large to 

 justify us in the belief that C-shaped spicules will always be found 

 in the suckers of the Echinidae, as I have proposed to define the 

 term. 



With regard to the form here called Cottaldia, it may be added 

 that the specimen was collected by the ' Challenger,' and that, 

 therefore, it was determined by Prof. Alex. Agassiz ; a reference to 

 that naturalist's report will sufficiently prove that he has had con- 

 siderable difficulty in finding a place for the species ; that difficulty 

 cannot, however, extend to its general position, now that the 

 spicules have been examined, and been found to be of the bihamate 

 type (Fig. 2). 



With regard to the Diadematidae, we have to note that, if the 

 forms have been correctly united, there is not the same closeness in 

 the characters of the ambulacral spicules in this group as there is 

 in that of the Echinidae ; though we can imagine a connection 

 between the spicules of Echinothrix (Fig. 4), and those of Diadema 

 (Fig. 5) it hardly seems possible to associate with them those of 

 Micropyga (Fig. 7) or of Astropyga, which have so striking a 

 Holothurian facies, and no generalization can safely be made at 

 present for this division. 



When Mr. Stewart published his paper in 1865 he had been 

 unable to find spicules in the ambulacral tubes of Echinocidaris 

 (Arhacia). I, too, was for a time unable to find them, but at last 

 they were detected ; they are but scantily present, but are very 

 characteristic, being greatly widened in the middle, and frequently 



t Proc. Zool. Soc. Loud., 1881, p. 418. 



* Those marked with an asteiisik were not reported on by Mr. Stewart. 



