NO. 3 DEICHMANN : HOLOTHURIOIDEA ; PART I, DENDROCHIROTA 129 



The Velero material measures from 5 to 20 cm. ; the largest individu- 

 als in the M.C.Z. measure more than 25 cm. in length. 



The occurrence of this typical Chilean species in Peruvian waters 

 makes it impossible to decide whether this species or Pat talus mollis rep- 

 resents Lesson's troublesome form, Holothuria peruana. Possibly a care- 

 ful survey at Payta, the type locality for peruana, may show that only one 

 of the 2 species occurs there. Pattalus mollis Selenka does occur in 

 Payta (material in the M.C.Z. ), but A. chilensis also may possibly be 

 found there, for both species are known to occur in the same localities, 

 i.e., at Ancon, Peru, and at Station 828-38. 



Genus 3. PATTALUS Selenka 



Pattalus Selenka, 1868, p. 113. 



Diagnosis. — Large form (20 cm. or more) with up to 20 large tenta- 

 cles of almost equal size. Skin thick with numerous tube feet. Calcareous 

 ring with 5 tall rectangular radials, with posterior corners rounded into 

 low protuberances; interradials with broad low basal part and a long 

 anterior tooth, often concealed in the thick tissue. Dorsally a long stone 

 canal with small head; Polian vesicles numerous, hanging as a fringe 

 around the ring canal, a few are dichotomously divided. Other anatomical 

 features typical of the family. 



Spicules a few branched rods, feet with large end plate. Color reddish 

 brown with a pigment which is dissolved in alcohol ; specimens which have 

 been preserved in alcohol for a long time are uniformly dull brown. Shal- 

 low water. 



Type species. — Pattalus mollis Selenka. 



Remarks. — The genus is monotypic and seems not related to any other 

 form. It has in the course of time been confused with Athyonidium chil- 

 ensis (Semper) but is definitely different from that species. It may pos- 

 sibly be identical with Euthyonidium ovulum (Selenka), although it 

 seems impossible that the smaller inner tentacles should ever be able to 

 attain the size of those in the external circle. The 2 species have the same 

 reddish color with pigment which is extracted in alcohol. They differ as 

 far as our present material shows in the more heart-shaped interradials in 

 E. ovulum, with a short anterior tooth, while P. mollis has a remarkably 

 long anterior tooth on the interradials. Also E. ovulum seems to lack a 

 large, dorsally attached, stone canal which is so characteristic a feature in 

 P. mollis. The large P. mollis is extremely common in Peru and is also 



