Genera of Recent Gly peas t fouls. G03 



branched^. This group has long been known as the 

 Scutellidse^ and while there are obvious reasons why it is 

 preferable that the type genus of a family should, if possible, 

 be one with Recent species, it would be worse than absurd to 

 abandon this ancient and euphonious name for no better 

 reason than that all known Scutellas are fossil. 



We thus find it desirable to recognize five families, which 

 seems like an excessive number for only fifteen genera, 

 especially since eight of the genera clearly belong to one 

 family. But I do not see how the number can be lessened 

 without obscuring real relationships. The Clypeastridte are 

 almost certainly the nearest of the families to the original 

 stock, and it is not hard to believe that the Laganidoe have 

 had a common ancestry with them. The Fibulariidse seem 

 to have been derived from the Laganid?e, or from its near 

 ancestor, by a process of simplification. The Arachnoididte are 

 certainly an old stock beginning on or near the Clypeastrid 

 branch and with no near relatives at the present day. The 

 Scutellidae are quite a distinct branch, though their origin is 

 probably very near that of the Laganidae, if not identical 

 with it. 



The five families and their constituent genera may be 

 distinguished by the following key. For convenience I have 

 included Scutella, the type genus of the Scutellidaj, although 

 it contains no Recent species. 



Auricles separate, each placed more or less clearly ou 

 the ambulacrum. 

 Test uot discoidal and seldom very flat ; anus not 

 supra-marginal; genital pores 5. (Clype- 



ASTEIDJE.) 



Poriferous areas of petals divergent, not incurved 



distally ; anus marginal Anotnolanthus. 



Poriferous areas of petals more or less incurved 



distally ; anus submarginal Clypeaster. 



Test exceedingly flat, discoidal ; anus supra- 

 marginal ; genital pores 4. (Arachnoidid^.) 



"With characters of the family Arachnoides. 



Auricles more or less fully fused into a single piece, 

 situated on the interambulacrum. 

 Actinal ambulacral furrows short and indistinct or 



* They are not branched in Alexandria, and often only indistinctly so 

 \n Ecliinarachnius. Duncan's suggestion that Alexandria "appears to 

 be an Arachnoides with a posterior notch " indicates that lie neither read 

 Pfeffer's description nor examined carefully the photograph given, in 

 which the iuterambulacra may be seen to be continuous. 



■iO* 



