NO. 3 DEICHMANN: HOLOTHURIOIDEA ; PART I, DENDROCHIROTA 103 



Spicules small 2-piIlared tables or derivatives of these. Feet with 

 large end plate and numerous curved supporting tables usually with a 

 well-developed spire, which in some forms, however, is completely re- 

 duced. Tentacles with delicate rods and often rosettes. Spicules gradually 

 reduced with age in certain species. 



Type species. — Thyone fusus (O. F. Miiller). 



Remarks. — The genus is well defined and corresponds to Pentamera 

 in Cuctimaria sensu latiore. It is sometimes almost impossible to identify 

 very young specimens of Pentamera and Thyone, as the latter passes 

 through a Pentamera-stage. Fortunately that stage seems to be so short 

 that one usually is able to find a few feet in the interambulacra. When 

 dealing with specimens less than 1 cm. long, it is, however, wise to con- 

 sider all the species of Pentamera and Thyone which are known in the 

 region under consideration. Often the spicules in the introvert and ten- 

 tacles differ in species which have spicules in the body wall which are 

 alike, but this character cannot always be relied upon. 



The type species is common in the eastern and northeastern part of 

 the Atlantic Ocean, while a closely related species is known from the 

 West Indies, but not reaching the coasts of New England ( T. fusus ? 

 Deichmann, 1930, p. 167). Another species with more robust tables, 

 often with a handle on the inner side of the buttons, is likewise known 

 from the West Indies (T. pseudofusus Deichmann, 1930, p. 168). 



From the Panamic region the Hancock Expeditions have secured 3 

 new species, while a fourth was in the M.C.Z., collected by the Stranger. 

 Of these 4 species, 2 are closely related to the West Indian species men- 

 tioned above. 



Key to the Species of Thyone s. str. Known from the 



Panamic Region 



1. Tables delicate with 4 to 8 holes; disk oval or squarish; 

 spire of medium height usually with 6 diverging teeth. Sup- 

 porting tables with spire completely reduced ; disk curved, with 

 4 central holes and ends expanded with a varying number of 

 minute holes 1. Thyone neofusus, new species 



1. Tables more or less stout; supporting tables in tube feet with 

 well-developed spire 2 



2. Disk of table medium-sized to large, round, squarish, or oblong, 

 with numerous holes and often with a few knobs or the entire 



