PROTENASTER AUSTRALIS. 169 



Hemiaster hickmani. 



Koehler, 1914. Ech. Indian Mus. Spat., p. 142. 



This is another of the Investigator's discoveries ard is the most unmis- 

 takable member of the genus. It was taken in considerable numbers in the 

 Gulf of Oman at depths of 689-833 fms. 



Protenaster. 



Pomel, 1883. Class. Meth. Ech., p. 36. 

 Type, Desoria australis Gray, 1851. Ann. Mag. Nat. Hist., (2), 7, p. 132. 



Pomel was quite right in separating the Recent Australian spatangoid 

 called Desoria australis by Gray from the Fossil Echini of the genus Linthia. 

 Gray's name Desoria being preoccupied cannot be used and Mr. Agassiz there- 

 fore put the species into the closely related genus Linthia. But unfortunately 

 the type of Linthia and the Australian species disagree in some very important 

 points and it is therefore unwise to treat them as congeneric. Protenaster 

 seems to be a rare genus except in the form of bare tests. I have never seen a 

 specimen in any other condition. 



The second species of the genus is known only from the bare test of the 

 holotype. Although obviously different from the Australian species, it seems 

 to be more nearly related to it, than to any other spatangoid. The Red Sea 

 spatangoid, called by Mazzetti (1894. Mem. Reg. Accad. Modena, (2), 10, 

 p. 221) Linthia assabensis is unidentifiable. The specimen was only 19 mm. 

 long and Mazzetti makes no reference to any genital pores. I think probably 

 it was a young individual of some of the Schizaster-like spatangoids. 



Key to the Species of Protenaster. 



Apex anterior; petals II and IV so divergent as to run at nearly right angles to the longi- 

 tudinal axis of the test; periproct not visible from oral side australis. 



Apex subcentral; petals II and IV much less divergent; periproct overhung by posterior 

 end of test and plainly visible from oral side rostratus. 



Protenaster australis. 



Desoria australis Gray, 1851. Ann. Mag. Nat. Hist., (2), 7, p. 132. 

 Protenaster australis Pomel, 1883. Class. Meth. Ech., p. 36. 



This is the Australian species, known only from Tasmania and the south- 

 ern coast of the continent. It seems to be a littoral species but specimens with 

 spines on are very rare. 



