J. Walter Gregory — On Rhynchopygus Woodil 301 



to be conclusively settled. Mr. Abbott has generously presented bis 

 specimen to tbe British Museum (Nat. Hist.). 



From the three specimens now known a tolerably complete 

 specific diagnosis can be compiled. Prof. Forbes' larger specimen 

 shows the anterior end with most of the anterior and right antero- 

 lateral ambulacra, a long sweep on the right side, and the peristome. 

 Mr. Abbott's specimen is the posterior end of an individual of about 

 the same size as the former, and it shows the projection in the 

 second figure which Prof. Agassiz regarded as the snout of a Pour- 

 talesian, to be the supra-anal rostrum of a Rhynchopygus. I am glad 

 thus to be able to demonstrate the correctness of Prof. A. Agassiz's 

 shrewd suggestion in regard to the larger of the fragments figured 

 by Forbes. 



Prof. Forbes' reason for referring these specimens to Echinarachnius 

 is not at all apparent. This genus had been well diagnosed by 

 Agassiz and Desor, 1 a few j'ears before Forbes wrote, and his own 

 specimens differed from this in nearly every particular. The absence 

 of actinal furrows, jaws, internal pillars and partitions ; the presence 

 of phyllodes ; the equality of the ambulacra, the tumidity of the 

 ambitus, and the excentricity of the peristome, together form a com- 

 bination of characters which necessitate the removal of the species 

 from Echinarachnius to a genus of a different order, viz. from the 

 Clypeastroida to the Spatangoidea. The marked floscelle shows that 

 it belongs to the Cassidulidas, and the transverse anus and supra- 

 anal rostrum prove that it belongs to the genus Rhynchopygus. 



The following specific diagnosis is based on the larger of the 

 specimens figured by Forbes and on that found by Mr. Abbott ; the 

 smaller of the original specimens may possibly belong to a distinct 

 species, as it is somewhat more tumid at the ambitus. 



Ehynohopygus Woodi (Forbes), 1852. 

 Outline seen from above elliptical, broadest at a quarter of the 

 length from the posterior end ; the supra-anal rostrum forms a con- 

 spicuous projection on the posterior margin. In elevation the 

 species is seen to be depressed, with the apex at the anterior third : 

 the anterior margin is sharper than the somewhat tumid lateral 

 margin. The posterior extremity is rendered apparently vertical 

 owing to the projection of the rostrum. 



The apical disc is situated at the vertex. 



Ambulacra subpetaloid, and open below : flush with the test : 

 pores distant. 



Actinal surface concave anteriorly, but bulging posteriorly. 

 1 Catalogue Eaisonne" des Echinides, Ann. Sci. Nat. Zool. (3) vol. vii. p. 133, 1847. 



