NO. 12 A NEW HOLOTHURIAN DEICHMANN 5 



From the Calif ornian form Thyone rubra H. L. Clark, Thyone 

 lugubris differs in its mottled grayish brown color and black tentacles, 

 contrasting strikingly with the vivid orange dorsum and tentacles and 

 snow-white ventrum of the northern form. The former reaches 

 normally a length of 30-40 mm., but very likely this is also true of 

 lugubris, as apparently most dendrochirotes continue their growth 

 after reproduction has set in. The spicules are slightly smaller in the 

 southern than in the northern form. 



Both species are viviparous, and the observations made by Dr. H. L. 

 Clark regarding the number of embryos developed, etc., in Thyone 

 rubra agree in all essentials with what has been found in Thyone 

 lugubris. 



The life history of the dendrochirote holothurians in which the 

 female develops the embryos free in the body cavity is rather imper- 

 fectly known. Horstadius (1926) has studied the very similar condi- 

 tions in the Mediterranean form Phyllophorus urna Grube, and was 

 the first to discover that the oviduct opened directly into the body 

 cavity, as one logically would expect, and apparently the eggs are set 

 free here at intervals. How they are fertilized — if, indeed, they are 

 fertilized at all — is unknown. When the embryos have reached a 

 length of several millimeters, they are apparently set free one or two 

 at a time, probably by breaking through the respiratory trees or 

 through the intestine. 



Both Thyone rubra and Th. lugubris belong definitely to the same 

 group, and when the genus Thyone finally is revised they will be 

 placed in a separate genus by themselves. They differ from the two 

 other species of Thyone with knobbed buttons which are known from 

 the tropical part of the Pacific coast of America in the presence of 

 the large buttons or plates with the external side covered by a huge 

 reticulum. The other species have either buttons with a strongly 

 spinous handle {Thyone gibber [Selenka]), or an external layer of 

 delicate reticulated baskets (Thyone panamensis Ludwig). 



From the West Indies no species so far has been reported which 

 has spicules similar to those which characterize lugubris and rubra, 

 nor does it appear, from a perusal of the literature, that they have any 

 relatives in other parts of the Pacific Ocean. 



