302 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 11 



That Mertensiothuria fuscocinerea is not the last growth stage of 

 M. pervicax is certain, since small individuals have been found having 

 the typical egg-shaped buttons with two narrow holes and sometimes one 

 or two pairs of minute holes. Also the Museum of Comparative Zoology 

 possesses huge individuals of typical M. pervicax. That the two species 

 are closely related seems evident and they may possibly represent dif- 

 ferent ecological forms. Judging from the literature and the available 

 material, M. pervicax ranges from Zanzibar and the Red Sea to 

 Hawaii. 



Re-examination of Holothuria pluricuriosa and comparison with 

 other individuals of Mertensiothuria fuscocinerea have proved that 

 several stone canals occur frequently in the latter species and that there 

 is an end plate in the retracted feet of the former; therefore Holothuria 

 pluricuriosa must be withdrawn as a synonym of Jaeger's old name. 



The Panamic material tends to be more dully colored, with larger 

 brown patches on the dorsum, than the typical ash-gray form from the 

 East Indies, and the black areas around the papillae are less clearly pro- 

 nounced. Nevertheless I do not feel justified in establishing a separate 

 form on the basis of the comparatively few specimens I have examined. 



6. Semperothuria n. gen. 

 (Holothuria languens group) 



Diagnosis: Slender forms, cylindrical to flask-shaped, of moderate 

 size, 10 to 15 cm, rarely 20 cm, with 20 small terminal tentacles and 

 feet in five scattered bands, cylindrical on the ventrum, more papilli- 

 form on the dorsum. Inner anatomy not remarkable; Cuvierian organs 

 well developed. 



Spicules a crowded layer of tables normally lacking the disk com- 

 pletely and with the tip of the spire ending in a few large teeth, form- 

 ing a single or double Maltese cross. Rarely a few tables also present 

 with four upward directed spines, or with a complete disk, with smooth 

 or spinous margin. In some species an inner layer present in the form 

 of scattered large, flat bars with dentate edge or a series of large lateral 

 holes. Ventral feet with large end plates, often surrounded by a number 

 of perforated oval plates ; numerous large supporting rods in the walls. 

 Dorsal papillae with reduced end plate and usually curved supporting 

 rods. 



Color varying shades of purplish gray or brown, paler around the 

 appendages and on the ventrum. Sometimes black dots scattered on the 



