THE SESSILE BARNACLES. 



159 



they seem to have a constantly greater number of spines of the 

 cirri. The tergiun is narrow, as usual in New England, with a 

 longer carinal margin than in English balanus. Plate 33, figure 6c, 

 is the tergum of a Bering Sea specimen, rather straighter than 

 some others. 



Externally the wall may be strongly ribbed (pi. 35, fig. 4, from 

 Albatross station 3289, Bering Sea), or cylindric with smaller ribs 

 like typical B. balanus (pi. 35, fig. 8, Cape Prince of Wales, Alaska). 

 Opercular valves of this lot are similar to plate 34, figures la to \c. 

 Pores of the wall like plate 35, figure 5. There is also a thin, 

 smoother form (pi. 38, fig. 20, Unalaska). The parietal tubes are 

 compressed, approaching the condition seen in plate 35, figure 2. 



PIG. 40. BALANCS BALANUS PROM ALASKA, a, LABRDM. 1), MANDIBLE, c, MAXILLA. 

 A, RIGHT CIRRUS i. e, STH SEGMENT OF THE ANTERIOR RAMUS OF CIRRUS in. /, MEDIAN 



SEGMENTS OF CIRRUS VI. 



They are solidly filled up near the summits, as in Atlantic speci- 

 mens. In the specimens from Albatross station 3289 the tubes are 

 larger, but are also filled up in the upper fourth or third. They 

 have no transverse septa in any part. 



The largest Bering Sea specimen seen measures 41 mm. in great- 

 est diameter. A cylindric specimen measures 33 mm. diameter, 

 30 mm. high. The large, boldly sculptured New England forms, 

 such as plate 34, figures 1, 2, 3, are wanting in Bering Sea collections. 



A specimen from Alaska, collected by the Corwin, has typical 

 mouth parts, except that the labrum has ~but one tooth. The first 

 cirrus has rami of 22 and 10 segments, the posterior ramus hardly 

 half the length of the anterior. Second cirrus with unequal rami 

 of 18 and 16 protuberant segments. Cirrus iii has rather numer- 



