286 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Tripneustes gratilla Loven. 



Echinus gratilla Linne, 1758. Syst. Nat., ed. 10, p. 664. 



Tripneustes gratilla Lov6n, 1887. Bih. K. Sv. Vet.-Akad. Handl., XIII, afd, 4, no. 5, p. 77. 



This well-known species was taken by the "Albatross" at the following 

 places, but none of the specimens call for any special comment, save the largest, 

 which is 145 mm. in diameter and pure white like esculentus. 



Fakarava, Paumotu Islands. 



Puako Bay, Hawaii, H. I. 



Honolulu Reef, Oahu, H. I. 



Honolulu Market, Oahu, H. I. 



Clarion Island, Eastern Pacific Ocean. 



Station 3876. Off Lahaina Light, Maui. Bott. temp. 74°. 28-43 fathoms. 

 S., g. 



Twenty-seven specimens. 



Gymnechinus. 



Mortensen, 1903. "Ingolf" Ech., pt. 1, p. 115. 

 Type-species, Echinus Robillardi de Loriol, 1883. Mem. Soc. Phys. et Hist. Nat. Geneve, XXVIII, 



no. 8, p. 23. 



The remarkable abactinal system of Echinus Robillardi is easily sufficient 

 ground for establishing a new genus. Mortensen considers this feature over- 

 shadowed by certain peculiarities of the pedicellariae and the bare buccal mem- 

 brane, and consequently includes in his genus two species {darnleyeiisis and 

 inconspicuus) which I have placed in Nudechinus. He has however described 

 two species {pulchellus and versicolor) which agree with Robillardi in the 

 extraordinary abactinal system (see Dan. Exp. Siam: Ech., p. 113 et seq.) and 

 there are two others in the M. C. Z. collections. There are thus five species 

 which boloiifi; in (lymnochinus, all characterized by the fact that unlike any 

 other known iCchini, oculars I and II are in contact with the periproct. As 

 correlated characters, it may be mentioned that the buccal membrane is thin 

 and bare (save for the jH-imordial ambulacrals), the globiferous pedicellariic have 

 a tubular blade ending in a single prominent tooth and the test is distinctly 

 flattened. In connection with the excentric position of the periproct. which 

 lies almost wholly on the right hand side of the antero-posterior axis, it is not 

 uncoinnion ti) lind eitiicr genital 3 or genital 4 excluded from the periproct by 

 the two ndjoininp; ^;o!iitals. 



