284 PEOP. p. M. dtjistcan's revision op the 



Genus Potjetalesia, A. Agassiz, 1869, Bull. Mus. Oomp. Zool. 

 i. p. 272 ; 1872-4, Revision, p. 344. Wyville Thomson, 1874, 

 PTiil. Trans. Boy. Soc. vol. clxiv. pt. 2, p. 747. Loven, 1883, 

 Pourtalesia, p. 82. 



Test small or rather large, thin or moderately thick, long, flask- 

 shaped, with a deep inversion of the anterior face, at the lower 

 part of which is the peristome ; with a rostrum produced poste- 

 riorly and inferiorly, the periproct being above the rostrum. Test 

 subcircular or broadly expanded in front profile, or generally 

 tumid at the sides, flatter actinally, and slightly depressed 

 abactinally. 



Apical system very excentric in front, disjunct, with four basal 

 plates perforated by the genital ducts; sutures fused ; madreporite 

 in the right anterior, and often between or in the other basals ; 

 anterior and antero-lateral radial plates aborted more or less ; 

 postero-lateral radials separated by some plates of the odd inter- 

 radium and disconnected from the basals by plates of the postero- 

 lateral and odd interradia. 



Ambulacra apetalous, uniporous, with large wide plates ; the 

 anterior large, deeply inverted, forming the peristomial upper 

 margin ; antero-lateral flush, placed far forward, neai'ly trans- 

 verse ; postero-lateral flush, very long, may become discontinuous 

 actinally by the interposition of plates of the postero-lateral in- 

 terradia ; the antero- and a disconnected part of the postero- 

 lateral ambulacra from the lower margin of the peristome, or the 

 antero-lateral may be crowded out. 



Interradia with unequal, mostly large, plates ; the antero- 

 lateral with a narrow, tall, peristomial plate in one zone (5) and a 

 small plate in zone a, which may not enter the margin ; the postero- 

 lateral meeting abactinally at the median line, and also actinally, 

 or only abactinally, not entering the peristome ; the second and 

 third plates of zone h of the right postero-lateral area united ; the 

 posterior interradium touching or not the peristome, discontinuous 

 or continuous, amphisternous. 



Peristome anterior, more or less vertical, at the bottom of the 

 anterior inversion. Periproct above the rostrum. A subanal 

 fasciole around the posterior rostrum. Pedicels similar, pointed, 

 without disks. Spheridia uncovered, numerous, in the lateral 

 ambulacra only. Spines short, slender, fenestrated, often spatulate 



