REPORT ON THE ECHINOIDEA. 131 



and the like througli Aerope, Aceste, and Cionohrissus, we can as readily trace the affinities 

 of the family to the Spatangina proper through such genera as Palaotropus, Genieo- 

 patagus, and Homolampas, and again to the Galeritidse and Echinolampadge through such 

 genera as Uy-echiniis and Cystechinus, while the many-sided affinities of the Pourtalesige 

 to the Ananchytidse, Dysasteridse, and sucli genera as Cardiaster, Holaster, Toxmter, and 

 the like have been more or less insisted upon in the comparative description of the several 

 genera of the family. 



The fact that this group of Pourtalesise has existed undisturbed since the Chalk, and 

 has been modified in so many different directions, makes this family one of the most 

 interesting studies among the Echinids as far as relates to the affinities of the different 

 groups of Spatangoids ; and their examination has done much to bring out the close 

 relationship existing between apparently most distant forms in the study of the fossil 

 genera thus far discovered ranging from the Chalk to the present time. 



The Ananchytid and at the same time the Galeritid affinities of the family ai-e best 

 shown in the structure of Cystechimis, in which we have a slightly sunken actinostome, no 

 fascicles, a disconnected apical system, the plates of the test of nearly equal size in the 

 ambulacra and interam1)ulacra, a flat actinal region, a high conical test, and in some species 

 a tendency in the plates surrounding the actinostome to develop into bourrelets or into an 

 indistinct posterior labium. Such a genus as Urechinus, on the other hand, although 

 most closely allied to Cystechinus, strikingly shows much more normal Spatangoid 

 affinities-; and such a genus as Calymne, while retaining structural features of Cystechinus, 

 such as the uniform size of the coronal plates in all the areas, has an elliptical test, a 

 strongly-marked actinal keel, again a most Ananchytid apical system, simple ambulacral 

 pores, a circular actinostome, and on the other side, the rudiments of a peripetalous 

 fasciole across the anterior extremity, a feature onty found in those Spatangoids differing 

 most widely from such genera as recaU the Echinolampadse or Clypeastroids. 



Through Homolampas and Argopatagus, which at first glance so greatly re- 

 semble Spxttangus proper, we can readily trace the relation of the Pourtalesife to the 

 Spatangina. The simple ambulacral pores, the rudimentary petals, and the compara- 

 tively large ambulacral plates are Pourtalesian features, while the structure of the 

 actinal surface, the presence of a subanal and perij)etalous fasciole (in Homolampas 

 fulva), the great development of some of the primary tubercles, and the jirominently 

 labiate actinostome, place this genus in close proximity to such genera as Lovenia, 

 Maretia, Eupatagus, and Metalia. 



Genicopatagus, on the contrary, shows most markedly the affinities of the family to 

 Spatangoids with a prominent labiate actinostome ; to such genera as Holaster, Cardiaster , 

 and Toxaster the group becomes allied from the structure of the ambulacral areas above 

 the ambitus ; while the remarkable affinities of this genus to Paleopmeustes and PalcBO- 

 tropus, from the structure of the ambulacral petals, as well as the total absence of fas- 



