76 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 8 



The introvert (the thin-vvalled skin between the base of the tenta- 

 cles and the anteriormost tube feet) often contains characteristic spicules. 

 In the species where the spicules are reduced gradually they are fre- 

 quently retained here. They usually resemble those found in the external 

 layer of the skin but are often more delicate and more complex. The 

 tentacles may be filled with large perforated plates or rods, or contain 

 minute rods or delicate plates, rarely a mixture of both. Rosettes seem 

 typical of certain species; they are apparently restricted to tropical and 

 subtropical forms and occur often in both the introvert and the tentacles. 

 In many cases the spicules in the tentacles become completely reduced 

 with advancing age. 



Family I. Gucumariidae 



Key to the Genera of Gucumariidae Known from the 



Panamic Region 



1. Body more or less globose, covered by large, reticulated scales. 

 Deepwater forms Sphaerothuria Ludwig 



1. Body not globose, not covered by large, reticulated scales. . 2 



2. Spicules spinous crosses. Deepwater forms 



Staurocucumaria Ekman 



2. Spicules not spinous crosses 3 



3. Feet restricted to ambulacra 4 



3. Feet also found in the interambulacra 7 



4. Feet retractile, soft, with end plate reduced or lacking. Spicules 



plates or buttons, often reduced 



1. Cucumaria Blainville (partim) p. 77 



4. Feet not retractile 5 



5. Skin covered by huge reticulated plates and smaller spicules. 

 Calcareous ring at most with short posterior prolongations. 

 5. Leptopentacta H. L. Clark p. 92 



5. Skin not covered by huge reticulated bodies. Calcareous ring 

 with long posterior prolongations 6 



6. Spicules 2-pillared tables, spire sometimes reduced. Feet with 

 large end plate. Spicules rarely reduced. 2. Pentamcra Ayres p. 84 



6. Spicules knobbed buttons, or irregular. Feet with large end 

 plate 3. Neopentamera, new genus p. 90 



7. Feet occur in interambulacra but chiefly in the dorsal ones. 8 



