112 



BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



and narrow. There is a short adductor ridge, not united with the 

 articular, and not extending upon the lower fourth or third of the 

 valve. The lateral depressor muscle lodges in a deep cleft. The 

 width of the scutum varies rather widely, and the tergal side is 

 abruptly deflected. 



The tergum is relatively large, wider than the scutum, and a trifle 

 shorter. It is flat, with slight growth-lines and no furrow to the 

 spur; the latter stands close to the basiscutal angle, is very short, 

 truncate, and Iroad, one-half to one-third the width of the valve. 

 Inside there is a moderate articular ridge, defining a broadly open 

 articular furrow; the scutal border is not inflexed. Crests for the 

 depressor muscles are sharp and numerous. 



The labrum (fig. 27&) has three rather strong teeth on each side. 

 Palpi substantially as in B. ampliitrite (See p. 93, fig. 19e). 



Fig. 27.— B. teigonus. West Indies, a, mandible, b, labeum. c, maxilla. 



Mandible (fig. 27a) with four teeth and an irregular lower point. 

 MaxiUa (fig. 27c) with seven or eight spines between the upper and 

 lower large pairs, which stand upon very shght projections. 



Cirrus i has rami of 20 and 9 segrhents, the posterior ramus Jialf as 

 long as the anterior, its segments moderately protuberant. Cirrus ii 

 with 10 and 8 segments (West Indies), or 13 and 9 segments (Cape 

 St. Lucas, Lower California). Cirrus iii having 15 and 12 segments, 

 the anterior ramus 4 segments longer. The lower segment of the 

 pedicel is very broad. The segments of both rami are convex an- 

 teriorly, and armed with thorn-shaped teeth. Smaller teeth, grad- 

 ing down to minute tubercles, are on the adjacent outer face of the 

 segment. These may be numerous, as in the West Indian individ- 

 ual figured (fig. 28a), or few, as in that from Cape St. Lucas (fig. 2Sd). 

 The distal two segments of the anterior ramus, and four of the pos- 

 terior, have no teeth. The inner faces of the toothed segments of the 

 anterior ramus are smooth, but those of the posterior ramus have some 

 or many long spines. Cirrus iv is long, like the following cirri, but 

 about six segments near the middle of the outer ramus have small 



