NO. 3 DEICHMANN : HOLOTHURIOIDEA ; PART I, DENDROCHIROTA 135 



Remarks. — The species is closely related to Phyllophorus destichadus 

 Deichmann from the West Indian waters. It differs in the presence of 

 supporting tables in the feet and in minor details of the calcareous ring 

 and the spicules. 



A species with somewhat similar spicules was described from Hawaii 

 by Fisher, 1907, and is now referred to Neothyonidium (Deichmann, 

 1938, p. 382). The Hawaiian species has tentacles in 2 separate circles 

 and of 2 different sizes, and the calcareous ring is of another type, with 

 long narrow interradials which are firmly joined to the radials, not over- 

 lapping them. 



Family III. Psolidae 



Diagnosis. — Dendrochirota with part of the ventral side developed as 

 a thin-walled sole, with feet along the margin and in many forms also 

 along the odd ambulacrum of the sole. Dorsal side (including the oral 

 and anal ends) covered more or less completely by scales; in certain 

 genera some scales are perforated for the passage of tube feet; in one 

 genus no feet are developed on the dorsal side. Tentacles 10 (15 in one 

 genus), the 2 ventral ones are often smaller; in the few deep water forms 

 the tentacles are almost finger shaped, with few or no branches. Cal- 

 careous ring simple; retractors of unequal length; gonads in 2 tufts on 

 the dorsal side opening on a papilla behind the tentacles. 



Spicules in sole, perforated plates or buttons, smooth or knobbed ; in 

 some forms the external deposits may be cup shaped, in others gradually 

 transformed into reticulated bodies ; in certain species the spicules become 

 scarce with age. Feet with end plate and a varying number of supporting 

 rods or plates. Dorsal side with or without a layer of spicules outside the 

 scales, as grains, cups, hourglass-shaped bodies, plates, etc. Dorsal ap- 

 pendages, if present, with or without end plate and supporting rods or 

 plates. Tentacles with or without perforated plates or rods; sometimes the 

 spicules disappear in older individuals; a few forms have rosettes. 



Remarks. — The family comprises about half a dozen genera and 

 represents a rather interesting series of evolutionary steps. Of the 3 genera 

 which are known from the Panamic waters Thyonepsolus represents un- 

 doubtedly the most primitive group, indistinctly separated from Psolid- 

 ium, while the highest evolutionar>' stage is represented by the genus 

 Psolus. The inner anatomy of the 3 genera is very similar. The most 

 striking difference is that in the 2 first-named genera the third loop of the 



