238 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



notch in the crest, and in the outer part resolves itself into two laterally elongate 

 tubercles placed side by side. 



The structure of the arm bases and of the arms is in general the same as that of 

 0. serripinna. The synarthrial tubercles on the articulations between the elements 

 of the IBr series and first two brachials are enormously developed, as in Perometra 

 diomedeae or in Amphimetra ensifer, but their apices, though they may be smooth as in 

 those species, are usually blunted and spread out laterally, bifurcated, or armed with 

 several blunt spines. Each half' proximal and distal of the synarthrial tubercle 

 may be at the tip armed with a sharp tubercle, the two tubercles pointing away from 

 each other at a considerable angle, or the proximal half of the synarthrial tubercle may 

 distally be laterally spread out and fanlike or dentate, and the distal half almost or 

 quite unmodified. The synarthrial tubercle on the articulation between the first two 

 brachials as a rule departs more widely from the normal than that on the articulation 

 between the elements of the IBr series. The IBr axillary has a usually very long and 

 prominent tubercle on either side of the distal apex. 



The second and following brachials have the distal edge everted, standing out at 

 right angles to the dorsal surface as a very high finely spinous crest. On the earlier 

 segments this crest is laterally narrow so that it appears as a high tubercle which may 

 be slightly broadened or chisel-shaped at the tip, or may be bifurcate or coarsely 

 dentate. After the first syzygy this process gradually broadens laterally so that after 

 the second syzygy it comes to involve the entire distal border of the brachials, which 

 stand out as very high more or less irregularly scalloped or dentate finely spinous 

 vertical frills. The earlier narrow projections are usually divided up into a few large 

 tubercles, but the broad later ridges are more uniform and more regular. 



The pinnules in general resemble those of 0. serripinna, but they are very much 

 more ornate. PI is 5 mm. long, very slender, with 14 segments of which the distal 

 are considerably elongated, and the outermost 5 or 6 have high carinate processes 

 involving the distal third or half of the median dorsal line. P 2 is 7 mm. long with 14 

 segments which in the distal portion are rather longer than is usual in 0. serripinna. 

 The processes in the middorsal line are much longer and larger than in 0. serripinna, 

 after the first 4 or 5 segments being a high uniform carination of the whole outer edge 

 of the segment of which the crest is parallel with the longitudinal axis of the pinnule, 

 and in the outermost 6 or 7 bifurcated, although not involving so much of the seg- 

 ments. The ventrolateral edges of the segments are as in 0. serripinna. The pinnules 

 following have the distal edges of the segments beyond the second greatly produced, 

 especially in the middorsal line, this production in lateral view appearing like long 

 overlapping spines such as are seen in the distal parts of the arms of the species of 

 Asterometra or of Stylometra. The distal pinnules, so far as they are preserved, do not 

 appear to differ in any way from those of 0. serripinna. 



The size is the same as that of 0. serripinna. 



Notes. One of the 18 specimens from which the preceding description was drawn 

 up lacks P a on both the arms arising from one of the IBr axillaries. 



Locality. Investigator station 171; entrance to Palk Strait; Point Pedro, Ceylon, 

 bearing SSE, about 3 miles distant; 9-13 (or 11-15) meters; sand; March 23, 1894 

 [A. H. Clark, 1912, 1918] (18, U.S.N.M., 35319; I. M.). 



History. This species was described by me under the name Oligometra serripinna 



