426 Reviews — Prof. C. Schuchert — Palaeozoic Stelleroidea. 



of North America. The account of the later forms, of the ophiurids 

 and their allies, and of the foreign material is mainly compilation, 

 and that it is no more is due to change of circumstances since the 

 work was begun. Still, an intelligent compilation may he valuable 

 as a summary of our knowledge, and certainly it is a great con- 

 venience to have had the literature so thoroughly ransacked for us. 



The rather barbarous name Stelleroidea, adopted from Gregory, 

 is intended to comprise all those animals generally known as 

 Asteroidea and Ophiuroidea, with a number of other forms evidently 

 allied to them but apparently forming distinct lines of descent, and 

 therefore not properly to be placed in either of those Classes. To 

 cover the same conception Mr. W. K. Spencer has restricted the name 

 Asterozoa, which originally had a still wider content. 



We can trace within known geological time the broad lines of 

 development that gave rise to the modern Ophiuroid type, but the 

 other groups, it is clear, already coexisted in fairly definite forms at 

 the earliest period from which we have any traces of Asterozoa 

 at all. That period is the Middle Ordovician, but the abundance and 

 diversity of starfish life then appearing make it quite clear that 

 there must have been ancestors provided with skeletons capable of 

 preservation. Before we can advance much further the fossils of 

 those ancestors must be found. They will decide between several 

 conflicting theories. Professor Schuchert is led by various considera- 

 tions to regard his new genus Hudsonaster as the most primitive 

 known form. Besides ambulacrals and adambulacrals this contains 

 inframarginals, supramarginals, and a dorsal radial series, but it has 

 no accessory plates. The structure is simple, that is obvious ; but 

 this simplicity may be the result of specialization from a less 

 definitely constructed ancestor. Professor Schuchert, however, does 

 not think so, but imagines an ancestor more simple still. It all 

 sounds very logical, but one is left wondering what the creature did 

 for a living. There is also a curious want of harmony with the facts 

 of embryology as regards the terminals, and one can hardly believe 

 that there was so striking a difference in this fundamental point 

 between the earlier Asteroidea and their modern descendants. Even 

 Professor Schuchert seems to have his doubts. I would also venture 

 a doubt as to his comparison with Echinoidea ; at any rate it is 

 far from certain that "the ambulacrals" of Echinoidea are the 

 "same ossicles as in Stelleroidea", or that the " interambulacrals = 

 adambulacrals of Stelleroidea ". 



It is not possible here to enter into a critical examination of the 

 systematic descriptions, but I must not leave to another the un- 

 gracious task of pointing out that the new species Hudsonaster batheri 

 is based on the imprint of the apical face of Tetr aster wyville-ihomsoni. 

 I told Professor Schuchert this many years ago when I sent him the 

 squeeze for study, and my verdict is now endorsed by Mr. W. K. 

 Spencer from his renewed examination of the original specimens. 



Congratulations to Professor Schuchert on having at last got this 

 laborious piece of work into the world. 



F. A. Bather. 



