REPORT ON THE ECHINOIDEA. 3 



With regard to the further subdivision of the Palseechiuoidea, the subdivision pro- 

 posed by Zittel into Cystocidaridse, Bothrioeidaridse, and Perischoechinidse, seems to 

 represent well our present knowledge of the group. The further subdivision, how- 

 ever, of the Perischoechinidse into Lepidocentrid^, Melonitidse and Archseocidaridae seems 

 somewhat doubtful. The Archseocidaridse, at any rate, and the Palgeechinidse 

 (M'Coy) appear to form most natural subdivisions. The Melonitidse and Lepidocentridse 

 hardly seem to be sufficiently distinct to be separated into different groups; and the 

 Palseechiuoidea, as a whole, can hardly be contrasted, after what has been said of the 

 structure of the test, to all the I'emaining types of Echinoidea, as is proposed by Zittel 

 and other palaeontologists. 



Both in the Desmosticha and in the Petalosticha the difficulties of properly combining 

 the subdivisions adopted on the one side by palaeontologists, and on the other ]iy those 

 who have mainly studied recent Echinids, are very great. 



The groups recognised by both, and concerning which there seems to be but httlc 

 question, are the Cidaridse, the Salenidse, and the Echinothuridae. The other subdivisions, 

 the Arbaciadae, the Diadematidae, the Echinometradae, and the Echinidae, which are in 

 addition recognised by writers on recent Echinids, are by palaeontologists limited to the 

 Diadematidae and the Echinidae. This limitation seems scarcely warranted by our know- 

 ledge of the recent Echinids, while on the other hand our information regarding the 

 structure of the apical and of the actinal systems of the greater number of the fossil 

 genera is not accurate enough to enable us to place many of them with any certainty 

 into the families adopted by those who have limited their studies to recent species. But . 

 such groups as the Arbaciadae and Echinometradfe, if not of the same systematic value as 

 the subdivisions Cidaridae, Diadematidae, and Echinidae, are certainly as important as the 

 Temnopleuridae and Triplechinidae. 



As regards the Clypeastroids, the agreement is quite close. We have only to add to 

 the families recognised by writers on recent species the Galeritidae and the Conocly- 

 peidae, which are represen.ted by a single recent species only in each group, leaving the 

 following recognised among the Clypeastroids — the Galeritidae, the Conoclypeidae, the 

 Euclypeastridae, and the Scutellidae. Among' the Petalosticha the larger subdivisions of 

 the recent species are the Cassidulidse, still further subdivided into the Echinoneidae 

 and the Nucleolidae ; and the Spatangidae, with the Ananchytidae, the Spatangina, the 

 Leskiadae, and the Brissina. The separation of the Holasteridae, as contrasting with 

 the Spatangidae as a distinct family by some palaeontologists, seems hardly justified from 

 our present standpoint, and it certainly seems more natural to consider the 

 Dysasteridae and the Ananchytidae as sub-famiUes of the Spatangidae ; the structure of 

 the Pourtalesiae and of other recent Ananchytidae seeming to render a separation into 

 Holasteridae and Spatangidae unadvisable. 



