NO. 3 DEICHMANN: H0L0THURI0IDEA;PARTI, DENDROCHIROTA 127 



Genus 2. ATHYONIDIUM, new genus 



Eucyclus Lampert, 1885, p. 290.— Theel, 1886, p. 268.— Ludwig, 1887, 

 p. 1239 (reprint p. 23). Name preoccupied. 



Diagnosis. — Large foiins (25 cm. or more) with thick, soft skin and 

 numerous stout feet. Tentacles 5 large external pairs and 5 small inner 

 pairs. Calcareous ring with 5 stout, almost rectangular radials and 5 in- 

 significant interradials, often completely concealed in the tissue. 

 One large dorsal stone canal, often branched and one or two tufts of 

 smaller stone canals with minute heads. Numerous tufts of branched 

 Polian vesicles. Inner anatomy seems otherwise quite typical of the family. 



Spicules large well-developed end plates, a few perforated spinous 

 rods; tentacles with few rosettes in the younger individuals. Color gray- 

 ish mottled to almost black, ventrum paler, tentacles dark. Shallow-water 

 forms. 



Type species. — Athyonidimn chilensis (Semper). 



Remarks. — The genus is monotypic and related to Thyonidium and 

 Euthyonidium, but the strikingly reduced interradials give it a position 

 almost unique among the Phyllophoridae. Very little can be said about the 

 spicules, as they are reduced even in small individuals (5 cm. long). They 

 may be present in still younger specimens, and one would expect them to 

 be tables, possibly with the spire reduced. 



Athyonidium chilensis (Semper) 



Thy one (Stolus) chilensis Semper, 1868, p. 241, pi. 40, figs. 3-6. — Lam- 

 pert, 1885, p. 156.— Theel, 1886, p. 139. 

 Eucyclus duplicatus Lampert, 1885, p. 250.— Theel, 1886, p. 268. 



Diagnosis. — As for the genus. 



Type. — Possibly in Germany. 



Type locality. — Coast of Chile. 



Distribution. — From Chile to Ancon, Peru. 



Depth. — Shallow water, at tidemark, in sand. 



Specimens examined. — The following material from the Allan Han- 

 cock Expeditions: 



828-38. San Juan Bay, Peru, shore, February 8, 1938, numerous speci- 

 mens. 

 831-38. Independencia Bay, Peru, shore, February 9, 1938, 3 specimens. 



Also the following specimens in the IVLC.Z. : 21 from Talcahuana, 

 Chile; 3 thrown up on the beach in Ancon, Peru, with Pattalus mollis. 



