NO. 3 deichmann: holothurioidea; parti, dendrochirota 137 



Spicules in sole perforated plates, knobbed or smooth, some may form 

 shallow baskets; feet with end plate and perforated supporting rods or 

 plates. Dorsal side with a varja'ng number of large towerlike deposits, 

 reduced with age, in some species shorter, approaching the shape of grains; 

 also hourglass-shaped bodies and curved plates. Feet with a small end 

 plate or none, and the walls supported by curved squarish plates, some- 

 times reduced to crosses and rods. Tentacles with heavy perforated plates 

 and smaller plates and rods, in some species rosettes. Shallow-water forms. 



Type species. — Thyonepsolus nutriens H. L. Clark. 



Remarks. — The genus seems to be restricted to the American waters. 

 The type species is known from Monterey Bay, California, and south- 

 ward to Santa Cruz Islands ; another species is known from the West 

 Indian seas, while 3 occur in the Panamic region and adjacent waters. 

 Two of these are here described as new. The type species is known to be 

 viviparous; the life histories of the other species are yet unknown. 



Key to the Species of Thyonepsolus Known from the 

 Panamic Region and the Californian Waters 



1. Dorsal scale covering incomplete in the midline (in the adult 

 individuals). Scales numerous and small; dorsal feet numer- 

 ous; external layer of spicules well developed. Sole with large 

 perforated plates and an outer layer of flattened baskets. Per- 

 forated plates in tentacles decreasing in size, no rosettes. Vivip- 

 arous; carries its large eggs in pits on the back. Californian 



waters (and Galapagos?) 



1. Thyonepsolus nutriens H. L. Clark 



1. Dorsal scale covering complete in the midline. Dorsal feet not 

 remarkably numerous ; external layer of spicules not remark- 

 ably crowded, varyingly developed. Sole without external layer 



of flattened baskets. Panamic waters 2 



2. Tentacles with rosettes and delicate rods besides heavy narrow 

 rods; plates in sole with indented margin. Midventral band 

 with feet crowded. . . 2. Thyonepsolus beebei Deichmann 



2. Tentacles without rosettes and delicate rods, only heavy plates. 

 Midventral band of feet with few feet 3 



3. Dorsal side with few (7-8) scales and fairly numerous feet. 

 Hourglass-shaped bodies large, irregular. Sole with knobbed 



plates. (Towers were not found in the type.) 



3. Thyonepsolus veleronis, new species 



