THE SESSILE BARNACLES. 



167 



not at all denticulated. Tlir al:r> h;ivo onliiiuc summits; tlieir sutural edges 

 are rather thick and distinctly crenated. Basis flat, calcareous, very thin, with 

 the surface slightly marked by radiating furrows, which furrows answer to 

 the radiating pores that occur in the bases of most species. 



FIG. 4!>. BALANUS CRENATUS, INGLEFIELD GULF, GREENLAND, a, LABRDM. 6, MAXILLA. 



C, MANDIBLE. 



According to Darwin : 



Mouth: Labi-urn with six teeth. Mandibles with the fourth tooth minute 

 or rudimentary, and the fifth generally confluent with the inferior angle. 

 Maxillte with generally, but not invariably, a small notch under the upper pair 

 of great spines. Cirri, first pair with the raroi very unequal in length, one 



FIG. 50. B. CRENATUS, INGLEFIELD GULF, GREENLAND, a, ANTERIOR PART OF THE FIF- 

 TEENTH SEGMENT OF OUTER RAMUS OF CIRRUS IV. ft, MEDIAN SEGMENT OF CIRRUS VI. 

 C, TENTH SEGMENT OF OUTER RAMUS OF CIRRUS III. 



ramus being nearly twice the length of the other ; in a large specimen having 

 a cylindrical shell the proportional numbers of the segments in the two rami of 

 the first cirrus were 10 to 23 ; in a small conical specimen the members were 

 only 8 to 13. The second cirrus has only two or three more segments than the 

 shorter ramus of the first pair. The third cirrus has one or two more segments 

 than the second ; but it is nevertheless decidedly longer than the second. On 

 the dorsal surfaces of both segments of the pedicel of the third cirrus, there 



