Genera of Recent Clypcastvouh. GOl 



Echinocyamus and Fibularia is mainly in tliis character, and 

 in these genera there is no reason to question the constancy 

 and systematic value o£ the difference. But having satisfied 

 myself that " Mellita stokesii " is only the young of Eucope 

 micropora, I am bound to say that I consider the internal 

 structure of the test of little taxonomic importance in the 

 Eucopes and their allies ; and having found the greatest 

 difficulty in making use of the character in Clypeaster and 

 Laganum, I have practically ignored it. 



The development of lunules in the more specialized clype- 

 astroids affords an obvious, constant, and most interesting 

 chai-acter ; but how much vreight is to be attached to their 

 manner of formation we do not know. Is Mellita sexies- 

 perforatus unique in the process of formation of its ambu- 

 lacral lunules? What significance does its characteristic 

 method have ? Is it of taxonomic importance ? Not being 

 able to answer these questions, I suggest them as worthy of 

 further investigation. The form of the petals is of course 

 a good character, but it is well known that even a single 

 species may show great diversity not only in the relative 

 length and width, but in the degree of closure at the distal 

 end. The position of the anus is an important character, 

 but as it shows relatively little difference in adults it is only 

 occasionally of practical value. The form of the test seems 

 to be the most easily modified character, and little weight 

 can be placed on it in determining relationships. Attention 

 has been called by De jMeijere to some interesting differences 

 between the spines of Laganum and Clypeaster ; but as I 

 have not found it necessary to use this character and have 

 not yet examined all the genera in this particular, I have 

 nothing to add to his valualale account (1904, 'Siboga' Ech. 

 pp. 103 et seq.). The pedicellarise also show characters 

 which may be useful for help in distinguishing species and 

 genera, but they have not seemed to me of sufficient im- 

 portance to take them into account here. 



There can be little question that Echinocyamus aiul Fibu- 

 laria belong in a family by themselves, but I do not think 

 this can be considered a primitive group. Such simplicity 

 of structure as they show is probably associated with their 

 small size, while their fused auricles and the structure of the 

 interambulacra strongly suggest nelationship to Laganum. 



In my judgment the most primitive of the Recent Clype- 



astroidais ^vohz^hlv Anomolanthus ov those species of Clypeaster 



with wide open petals such as C. ravenellii, A. Ag. In these 



forms the auricles are paired, well separated, and ambulacral 



Ann. d) Mag. N. Hist. Ser. 8. Vol. vii. -10 



