266 NEW STARFISHES AND OPHIURANS—VERRILL. vol.xvii. 



coarser and less even, and not so numerous; the primary interradial 

 plates are relatively much smaller and less distinct from the others; 

 the madreporic plate is finely caucellate ; the adambulacral plates bear 

 more numerous, stouter, and more angular spines; in the furrow-series 

 there are usually four or five spines; on the middle of the actinal sur- 

 face three to five stout, blunt, angular spines; and on the outer margin 

 usually three or four short, thick, angular, granule-like spines. 



Bemarks on the characters of the preceding families. 



The preceding families Archasteridte, Astropectinid?e and Pen- 

 tagonasterida^, as limited by Mr. Sladen,* are not well defined, nor 

 do the few characters given by him hold good in all cases. 



The existence of suijerambulacral plates has been supposed to be 

 characteristic of the Astropectinida? only, but they exist in several of 

 the genera referred to Arch aster idne, viz., Bytaster, Plutonaster, and 

 Pseudarch aster. 



The aproctous condition, supposed to be characteristic of the same 

 family, is unreliable, for in nearly all the genera referred to it by Mr. 

 Sladen there is a i^erfectly well defined dorsal or "anal" pore appearing 

 just as in the Archasterida?, and in some of the genera the pore is even 

 elevated on the summit of a dorsal cone or chimney {Psilaster, Ilyaster, 

 etc.). This pore serves in each of these families (and in Asterioidea 

 generally) for the discharge of the secretion of branched dorsal glandu- 

 lar organs, probably nephridial in function, situated above the stomach. 



Whether the central pore serves as a true anus in any of these star- 

 fishes is very doubtful, for the intestine is usually nearly or quite abor- 

 tive. In any case it is impossible to ascertain this point without actual 

 dissection of alcoholic or fresh specimens, which are often not avaihible. 



The distinctions between the Pentagon asteridiie and Archasteridfe 

 are also very faint and indefinite, for although the typical genera of 

 each group appear to be very different, there are many intermediate 

 genera now known, so that there is probably not one diagnostic char- 

 acter that can be given to separate the two groups as limited by Sla- 

 den. If the two families are to be preserved, it will probably be nec- 

 essary to change their limits and to transfer some of the genera. 



It would, perhaps, be more in accordance with a natural classification 

 to drop the family Archasteridie and distribute the genera referred to 

 it among those of the other two families. In such a system those genera 

 having distinct fascioles between the marginal plates and between the 

 infero-radial plates would belong with the Astropectinidse, while those 

 without fascioles would be placed in the Pentagonasteridse or Gonias- 

 teridte. 



By this rearrangement the former family would include mostly those 

 genera covered with true paxillte and parapaxillae, and the latter would 



* Voyage of the Challenger, xxx, pp. xxviii-xxxi, 1, 174, 260, 1889. 



