NO. 3 DEICHMANN: HOLOTHURIOIDEA ; PART I, DENDROCHIROTA 147 



anatomy typical of the family; third loop of the intestine seems always 

 to be attached in the right ventral interambulacrum. 



Spicules in sole plates or buttons, smooth or knobbed, in some forms 

 reduced with age, in others transformed into reticulated masses. Feet 

 usually with end plate and supporting rods. Dorsal side has besides the 

 scales often grains, rarely a few cups are present. Introvert and tentacles 

 with or without rods or plates; sometimes spicules reduced, in older in- 

 dividuals. 



Type species. — Psolus phantapus (Strussenfeldt). 



Remarks. — The genus comprises about 30 difiFerent species and repre- 

 sents apparently the most successful and widespread of the genera 

 included in the family. A number of the species are exceptionally large 

 (sole more than 10 cm. long) . The members of the genus occur in tropical 

 as well as in Arctic seas. 



The Hancock Expeditions have secured only one species, but 2 others 

 are discussed below to emphasize the diflferences between the species. One 

 represents a common form ranging from the Strait of Magellan to the 

 southern part of Bering Sea; the other, although hitherto known only 

 from the vicinity of Cape Horn, may possibly be expected in the southern- 

 most part of the Panamic region although it is not likely. 



Key to the Species of Psolus Known from the Panamic Region 

 AND West Coast of South America 



1. Dorsal scales large but few (2-3 between oral and anal valves) . 

 Oral and anal valves large. Small form. Spicules in sole 

 knobbed plates 3. Psolus diomedeae Ludwig 



1. Dorsal scales more numerous 2 



2. Spicules in sole slightly hollow buttons and plates with small 

 holes and large marginal knobs. Distinct oral valves. . . . 

 2. Psolus patagonicus Ekman 



2. Spicules in sole flat, mostly 4-holed buttons reduced with age. 

 Dorsal side with few large round grains; oral valves indistinct. 

 . . 1. Psolus squamatus (Koren), var. segregatus Perrier 



1. Psolus squamatus (Koren), var. segregatus Perrier 



Plate 30, Fig. 7 



Psolus squamatus (Koren), var. segregatus Perrier, 1905, p. 59. — 

 Ekman, 1925, p. 136, text figure 33. 



