554 RHYNCHOPYGUS PACIFICUS. 



Rhynchopygus pacificus 



! Pygorhynchus pacificus Ac, 1S63. Bull. M. C. Z.. T. p. 27. 

 ! Rhynchopygus pacijicus A. Ag., 1872, Rev. Ech., 1't. I. p. 153. 



PI. XV f. 1-2; PL XXXII. f. i-io ; PL XXXIII. f. is. 



Outline from above elliptical, angular, rounded anteriorly, somewhat more 

 pointed posteriorly; vertex and apical system coincident, slightly anterior ; 

 ambulacra] petals lanceolate, extending nearly to the edge, open at the ex- 

 tremity ; poriferous zones broad ; pores distant ; poriferous zones equally devel- 

 oped in all petals, except that the posterior zones of the posterior pair of petals 

 are much shorter than the anterior zones. Apical system small ; posterior geni- 

 tal pores somewhat more separated than the anterior pair ; madreporic body 

 slightly convex. Seen in profile, the outline is regularly arched to the ante- 

 rior extremity, and towards the posterior as far as the anal projection of the 

 test, placed about one third the height from the edge to the apex ; posterior lip 

 of anal opening depressed ; test sloping from it towards the edge, forming at 

 the same time a shallow anal groove. Aetinal surface nearly ilat, forming a 

 sharp angle with the sides of the test at the ambitus, sloping slightly towards 

 the sunken actinostome; mouth pentagonal, nearer anterior extremity than 

 apical system ; anterior bourrelets greatly developed, very prominent; poste- 

 rior bourrelets smallest, less prominent than odd interambulacral one. Phyl- 

 lodes large, commencing at a distance from the actinostome, with as many as 

 seven to nine pores on each side in the outer row of pores, standing out prom- 

 inently in the smooth, dagger-shaped band, extending from the anterior to the 

 posterior edge; this hand is broadest in the anterior ambulacrum, forming a 

 continuous star-shaped band round the actinostome. extending a short distance 

 in the lateral ambulacra, slightly beyond the ph\ llodes. uniting in the median 

 posterior interambulacral space, and gradually tapering (with angular concave 

 sides) towards the posterior edge of the test. The whole of this apparently 

 smooth band is covered by minute distant tubercles, carrying short, slender, 

 silk-like spines, and is irregularly pitted along the lines of the sutures of the 

 plates of the test. The tuberculatum of the abactinal surface is quite uni- 

 form, extending on the aetinal side but a short distance from the ambitus; 

 it then increases rapidly in size ; the pits surrounding the tubercles become 

 deeper and broader, attaining their greatest size immediately adjoining the 

 median aetinal band. The spines of the abactinal side are short, slender, 

 longitudinally striated, cylindrical, tapering; those of the aetinal side more or 

 less curved, especially the larger ones, which resemble more spines of Spatan- 



