124 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 8 



Genus 1. EUTHYONIDIUM Deichmann 



Euthyonidiu?n Deichmann, 1938, p. 380. 



Diagnosis. — Medium-sized form (length 10 cm. or less). Tentacles 

 definitely arranged as 10 large ones in 5 external pairs and 5 inner pairs 

 (or 5 single ones?)'^ which are smaller. Apparently all the tentacles ap- 

 pear at an early stage. Calcareous ring simple with tall rectangular radials, 

 posteriorly with short protuberances which may be interpreted as rudi- 

 mentary prolongations. Interradials well developed. 



Spicules small tables with oval to squarish disk, often with dentate or 

 branching margin ; spire low, 2-4 pillared often reduced to knobs or spines 

 or totally resorbed. Feet with large end plate and often a few small sup- 

 porting rods, i-arely with trace of being derived from tables. Introvert 

 with tables with numerous holes in the disk and spire often reduced. 

 Tentacles with rosettes and delicate rods. Spicules often reduced with 

 advancing age. Shallow-water forms, restricted to the tropical waters. 



Type species. — E. segiiroensis (Deichmann). 



Remarks. — From the West Indies 2 species are known, viz., the type 

 species and E. occidentalis (Ludvvig). From the Panamic region 2 species 

 are now known ; one represents the species which formerly was known as 

 Thyone ovulum Selenka, and the other, which is new, is closely related 

 to E. occidentalis from the West Indies. 



Key to the Species of Euthyonidium Known from the 



Panamic Region 

 1. Spicules oblong tables with dentate edge; spire 2 pillared, low, 

 often reduced to knobs or spines, or lacking. Color grayish. . 

 2. Euthyonidium veleronis, new species 



1. Spicules large tables with cross-shaped disk, often irregularly 

 laciniatcd ; spire mostly reduced to a few knobs or spines. Color 

 reddish brown. ... 1. Euthyonidium ovulum (Selenka) 



1. Euthyonidium ovulum (Selenka) 

 Plate 24, Figs. 1-7 



Stolus ovulum Selenka, 1867, p. 356, pi. 20, fig. 117. — Semper, 1868, 

 p. 66.— Lampert, 1885, p. 162.— Theel, 1886, p. 138. 



'^ The inner smaller pairs may possibly in some forms be found to be 5 smgle 

 tentacles which are deeply divided as Heding (1936, p. 23) has found It to be the 

 case in the type species of the closely related genus Thyonidium from the northern 

 seas. 



