76 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



lobed plates, rather irregular on dorsolateral area; carinals well marked, + form; 

 superomarginals + form, regular (not warped) ; abactinal and superomarginal spine- 

 lets short, spaced, tubercular or mobile, one to several per plate; interbrachial septum 

 small, almost wanting; gonads opening dorsally just above superomarginal plates. 



Remarks. — Tarsaster stoichodes, the type of the genus, was described by Sladen 

 in the Challenger report (1889, p. 440) and was based upon a single specimen taken 

 north of the Admiralty Islands in 150 fathoms. It was classified in the now defunct 

 Stichasteridae because the dorsal plates were arranged in longitudinal series. A 

 second species, T. distichopus (differing in having unguiculate pedicellariae and biserial 

 tube-feet), was described by the writer from the Straits of Macassar, 400 fathoms 

 (1919, p. 590). In attempting to classify " Sporasterias " mariana Ludwig, S. cocosana 

 Ludwig and S. galapagensis Ludwig from the Pacific coast of Mexico and Panamic 

 area, it became apparent that they were perhaps generically the same as Tarsaster 

 distichopus Fisher. I have had the advantage of making direct comparison of speci- 

 mens. All these species have the first pair of postoral adambulacral plates separated 

 interradially (or else in slight contact by the adoral corners) and thus resemble 

 Pedicellaster, where the separation is always complete and conspicuous. They all 

 differ from true Pedicellaster in having a prominent longiseries of inferomarginal spines 

 external to the adambulacral. 



Dr. R. Kirkpatrick, of the British Museum (Natural History), examined for me 

 the type of Tarsaster stoichodes and made photographs of the oral angle. Doctor 

 Kirkpatrick found, as shown by the photographs, that the first pair of postoral 

 adambulacral plates are in partial contact; that is, they touch interradially by the 

 adoral portion of the appropriate margin. In the other species which I have placed in 

 this genus the plates are separated, but in Ampheraster an analogous condition exists; 

 the plates may be either separated or in partial contact. In Ampheraster marianus 

 the largest specimen has the plates in contact, the other smaller specimens have them 

 separated. 



It has seemed best to segregate in Ampheraster those species which, while resem- 

 bling Tarsaster, have conspicuous unguiculate straight pedicellariae, a predominantly 

 monacanthid adambulacral armature, enlarged interbrachial superomarginal plates, 

 and no accessory inferomarginal spinelet or tubercle. 



The latter, in the American species of Tarsaster, is a good recognition character 

 and is constantly present in such distinct (perhaps subgenerically separable) species, 

 as alaskanus and cocosanus. Sladen does not describe it in the type but in the photo- 

 graph there appears to be an accessory inferomarginal spinelet above one of the major 

 spines. 



In Tarsaster as here limited the superomarginal plates do not exhibit the curious 

 instability characteristic of Ampheraster. The plates are of the conventional four- 

 lobed pattern and form regular longiseries. The distal plates are occasionally a 

 trifle warped. 



Tarsaster and Ampheraster are structurally in some respects intermediate between 

 Pedicellaster and the simpler Asteriinae. The skeleton above the inferomarginals is 

 very similar to that of typical Pedicellasterinae (which are now known to have some- 

 times unguiculate straight pedicellariae). The crowding of the tube-feet, in Tarsaster, 

 into two zigzag rows, or into four distinct series, follows a multiplication and shorten- 



