114 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 8 



Type locality. — Station 545-36, Puerto Refugio, Angel de la Guardia 

 Island, Gulf of Calif. 



Distribution. — From the upper end of the Gulf of Calif, to Mazat- 

 lan, Mex. 



Specimens examined. — The type and the following individuals from 

 the Velero Expeditions: 



465-35. Playa Blanca, Costa Rica, shore, February 8, 1935, 1 specimen. 



545-36. In Puerto Refugio, Angel de la Guardia Island, west of rock 



spit at river wash, shore, March 4, 1936, type and 4 paratypes. 



591-36. Port Escondido, L. Calif., Mex., shore, March 16, 1936, 2 



specimens. 

 844-38. Lobos de Afuera Island, Peru, shore, February 14, 1938, 1 

 specimen. 



Also a number of specimens in the M.C.Z. collection from Mazatlan, 

 Mex., shore, Situantanejo Bay, Mex., and Costa Rica, shore. 



Remarks. — It is with some doubt that the present material has been 

 referred to a new species, for the spicules are — aside from the absence of 

 heavy plates covered by a stout reticulum — highly reminiscent of those 

 found in Pachythyone pseudoluguhris, which is described below, and the 

 latter does actually occur in the same localities as Neothyone gibhosa. The 

 buttons have, however, more frequently 3 knobs on the external handle 

 and show little tendency to become elongate as in pseudolugubris where 

 the 2 central knobs frequently remain separate. 



Genus 10. PACHYTHYONE, new genus 



Diagnosis. — Small forms (few cm. long) with stout feet in 5 bands 

 and numerous in the interambulacra ; dorsally and toward the ends more 

 papilliform. Ventral tentacles smaller. Calcareous ring with short poste- 

 rior prolongations. Single stone canal, single Polian vesicle. Gonads form- 

 ing 2 tufts of few tubes. 



Spicules an external layer of oval buttons or plates with the external 

 side covered by a dense reticulum ; an inner layer of oblong 4-holed but- 

 tons regularly knobbed. Feet with end plate, reduced in the papilliform 

 feet; walls supported by supporting tables with numerous rods in the 

 reticulated spire; a few developed as plates. Introvert with oblong tables; 

 tentacles with heavy perforated plates which gradually become smaller 

 and more delicate in the branches. 



Type species. — Pachythyone rubra (H. L. Clark). 



