40 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



and the same is true for Xenaster and Agalmaster. The plate is also 

 known in Palseaster, Devonaster, Neopalxaster, and Pdlasterina. 



In multi-rayed phanerozonians the madreporite is unknown in 

 Lepidaster and Lepidasterella. In Helianthaster it is large, conspic- 

 uous, and situated on the edge of the disk, more actinal than abac- 

 tinal. On the other hand, in the cryptozonian multi-rayed genera 

 the madreporite is apparently always actinal and more or less large, 

 as in Palseosolaster and EcMnodiscaster. This plate is probably also 

 always actinal on large-disked Cryptozonia such as Palasteriscus 

 (plate enormously large), and Clieiropteraster (here small and situ- 

 ated near the mouth) . 



Among the five-rayed Paleozoic cryptozonians the madreporite 

 is known only in Monaster (large), Urasterella (medium), and J aelcel- 

 aster (small). In all it is always on the abactinal area. 



From this evidence we see that in the five-rayed Phanerozonia, 

 forms that are more or less rigid, the madreporite is always on the 

 dorsal or upper side of the animals, this being true for the deeply 

 stellate as well as for the pentagonal species. In the multi-rayed 

 genera, however, there is a marked tendency for this plate to move 

 outward to the edge of the disk. In the five-rayed cryptozonians 

 the madreporite so far as known is always dorsal, but in the large- 

 disked or pentagonal forms and the multi-rayed species this plate is 

 apparently always ventral. 



Spencer (1914:35-38) says that ''many Paleozoic Asterozoa do not 

 appear to have a madreporite" and he is "inclined to regard this, 

 in these old forms, as usually a primitive feature." The present 

 writer, it is true, states above that in more than half of the Paleo- 

 zoic asterids the madreporic plate has not been seen. This is due in 

 most cases, however, to poor preservation, and in others to the fact 

 that the plate is so much like the other disk plates as not to be dis- 

 tinguishable from chem. Spencer concludes further that it appears 

 that the madreporite originated on the ventral side, or at least was 

 marginal, in the primitive forms, and that it passed over in later 

 Asteroidea to the dorsal side. In Hudsonaster we have the most 

 primitive known starfish, and here in H. incomptus it is a large and 

 conspicuous plate on the abactinal side. Further, the evidence of 

 the Paleozoic starfishes (Phanerozonia), so far as the present writer 

 knows them, is that this plate is always dorsal in position, and he is 

 inclined to the view that all of them had the madreporite, that it 

 originated on this side, and that in later cryptozonian multiradiate 

 forms it moved outward to the margin of the disk or to the actinal 

 surface. In regard to the Auluroidea, the writer has seen the 

 madreporite so rarely that no deductions as to its original position 

 in these forms can be made. 



