NO. 3 DEICHMANN : HOLOTHURIOIDEA ; PART I, DENDROCHIROTA 115 



Remarks. — Only 3 species have been referred to the genus; all are 

 known from the western coast of North and Central Ameiica and two 

 are viviparous. 



Key to the Species of Pachythyone 



1. Color white ventrum and red dorsal side and ends. Spicules 

 slightly larger and robust ; plates in tentacles mostly knobbed. 

 1. Pachythyone rubra (H. L. Clark) 



1. Color mottled brown. Spicules more delicate; plates in ten- 

 tacles mostly smooth 2 



2. Supporting tables with strongly branching spire, even in the 

 ventral feet. ... 2. Pachythyone lugubris (Deichmann) 



2. Supporting tables with low spire, at least in the ventral feet. 

 3. Pachythyone pseudolugubris, new species 



1. Pachythyone rubra (H. L. Clark) 

 Plate 23, Figs. 10-12 



Thyone rubra (H. L. Clark), 1901, p. 166; text figures 1-5; 1901a, 

 p. 494. — Deichmann, 1939, p. 5 (passim) ; text figure 3. 



Diagnosis. — Small, robust form, few cm. long, with stout cylindrical 

 feet in 5 longitudinal bands and scattered in the interambulacra ; dorsally 

 the feet show some tendency to become papilliform. External and in- 

 ternal anatomy typical of the genus. Spicules an outer layer of oval 

 plates covered on the external side by a large reticulum; an inner layer 

 of mostly regular 4-holed buttons with 10 marginal knobs and usually 

 2 central knobs; often the button is lozenge shaped with an accessoiy 

 hole in each end. Feet with large end plate, reduced in some of the 

 dorsal feet, and numerous large supporting tables with a huge reticu- 

 lated spire; in some of the dorsal feet it covers almost the entire disk of 

 the supporting table. Introvert with oblong tables with more or less com- 

 pletely reduced 2-pillared spire, sometimes with a few teeth. Tentacles 

 with knobbed plates or rods. Apparently rosettes are not present. Color 

 bright orange-red dorsum and ends, ventrum pure white. (Color retained 

 in alcohol.) Viviparous; the body cavity of the female contains often 

 about half a dozen embryos of different developmental stages. 



Type.— M.C.Z. 



Type locality. — Monterey Bay. 



