ONITHIS CRASSISETOSA. 299 



and over the distal part of the fang of maxilla I. Maxillae I with the carrier- 

 plate equal in length and breadth; on each side incurved at the anterior end 

 and then convexly rounded caudad as usual; each half obliquely bent so as to 

 leave an anterior triangular area more elevated. The blade is short, broad 

 proximally, and rather abruptly narrowed at the middle to the fang, which is 

 neither long nor strongly curved. Right maxilla II with nine stout, blackish 

 teeth, of which the most anterior is decidedly largest ; the left outer plate with 

 seven teeth, of which the anterior one is enormous in comparison with the others, 

 appearing somewhat like the blade of maxilla I laut proportionately much broader ; 

 the inner plate has eight teeth which are stout and darkened, regular, the most 

 anterior not being larger than usual. The right maxilla III is a long, strongly 

 curved plate bearing twelve teeth; the right plate is considerably shorter but 

 is also strongly bent and bears ten teeth. Each maxilla IV is darkened and ele- 

 vated in a somewhat dentiform process at its anteromesal angle. (Plate 42, 

 fig. 3). The mandibles are well developed, with the masticatory plates visible 

 when in situ. These plates are large, hard, white, and strongly diverging, the 

 anterior margin of each incised and dentate near its middle. The stems are 

 narrowed caudad and are scarcely united anteriorly; they are conspicuously 

 darkened. (Plate 42, fig. 2). 



Localities. Off Central America: Sta. 4621 (lat. 6° 36' N., long. 81° 45' 

 W.). Depth 581 fms. Bottom of green sand. Bottom temp. 40.5° F. 21 Octo- 

 ber, 1904. Two specimens in tubes. 



Off Galapagos Islands: Sta. 3401 (lat. 0° 59' 0" S., long. 88° 58' 30" W.). 

 Depth 395 fms. Bottom globigerina ooze. Bottom temp. 43.8° F. One 

 incomplete specimen with hyahne tube attached to siUcious sponge rod as in 

 those from the preceding station, 28 March, 1891. 



From most other Pacific forms with simple branchiae and the anterior 

 crochets only bidentate, this species is most easily distinguished in having the 

 branchiae begin on the fourteenth parapodia, instead of the sixth in lepta, eighth 

 in macrobranchiata, seventeenth in pycnobranchiata, and twelfth or thirteenth in 

 hiatidentata. In the case of hiatidentata the relationship is undoubtedly very 

 close, as shown in structure throughout; but nmnerous differences in details 

 render the separation of the two forms necessary, especially in view of the fact 

 that specimens of the present species from two well-separated stations show con- 

 stancy in these differences. The present species is very much smaller, having 

 a maximimi diameter of only 2 mm., instead of 4.8 mm. in hiatidentata. At the 

 same time the dorsum in general is less strongly arched, and is narrowed at the 



