160 HAWAIIAN AND OTHER PACIFIC ECHINI. 



that the absence of a subanal fasciole is a fundamental character, for we have 

 already seen that this fasciole tends to disappear with age in Urechinus and we 

 know that this also happens in Spatangus at times. Moreover in Meoma the 

 subanal fasciole tends to disappear and the result resembles the lateroanal 

 fasciole of certain Hemiasteridae. 



Pedicellariae in the family are abundant and diversified, but it is difficult 

 to find any features characteristic of the family as a whole. Both Mortensen 

 and Koehler have published many figures of the various forms in different 

 genera, while contributions have also been made by de Meijere and Doderlein. 

 The globiferous pedicellariae, when present, often afford good characters which 

 may even be of generic value, while occasionally good specific characters are 

 to be found in the rostrate and tridentate pedicellariae, and more rarely in the 

 ophicephalous. 



Thanks to the careful and extended researches of Mortensen, the genera 

 in this family are now fairly easy to distinguish, so far as the Recent forms 

 are concerned but the Fossil forms need careful revision to determine whether 

 any of them are congeneric with species now living. The types of the genera 

 Pericosmus and Hemiaster are Fossil forms, but I can find no good reason for 

 separating the Recent species from them. The genus Linthia is also based 

 on a fossil species, but I fully agree with Pomel that the Australian spatangoid 

 long known as Linthia does not belong in that genus and is best treated as the 

 type of a new genus Protenaster. I cannot see that the proposed genus Pseuda- 

 batus is worthy of separation from Abatus, and I doubt the wisdom of recognizing 

 Tripylus and Tripylaster. Another very dubious genus is Prymnaster, which 

 is based on small specimens, probably immature, of species of Paraster. In 

 Paraster too belongs the Recent species called Linthia rotundata by Doderlein. 

 On p. 164 of his report on the echinoderms of the Charcot Expedition. Koehler 

 refers to a genus "Parabatus." I am unable to find any such generic name in 

 use and conclude it must be a slip of the pen. 



Key to the Genera of Hemiasteridae. 



No fascioles. 



Test markedly depressed, v. d. less than .40 length; petals nearly flush . . . Plntybrissus. 



Test moderately high, v. d. more than .50 length: petals (at least in 9 ) more or 



less sunken AviphipneusUs. 



Peripetalous fasciole present. 



Ambulacra H and IV dorsally, not petakrid and not sunken, the anterior series of 



pore-pain wanting 



Ambulacra 11 and IV dorsally more or less petaloid, or deeply sunken, the an- 

 terior series of pore-pairs present. 



