136 



BULLETIN 03, UNITED STATES NATIONAL MUSEUM. 



Compartments. The parietal tubes are filled up in the upper 

 part, rather large and square toward the base, where some short 

 lamellae from the outer lamina of the wall project into the lumen 

 much as in B. balanus. The tubes have no transverse septa. The 

 inner lamina of the wall is ribbed below the sheath, each rib crenu- 

 lated at the base, terminating in a septum to the outer lamina. The 

 sheath is long, smooth, and lies close to the wall, only very narrow 

 hollows in places below its edge. The radii are smooth, rather wide, 

 with extremely oblique, minutely jagged summits; lateral edges nar- 

 row, rather deeply denticulate. Ala? have also very oblique, smooth - 

 ish summits. Sutural edges deeply denticulate, the denticles hardly 

 crenulated. 



The basis is concave externally in the specimens seen. It is of 

 moderate, nearly equal thickness, distinctly porous, and in places has 



FIG. 37. BALANUS FLOS, a, LABRUM OK SPECIMEN FROM HUMBOLDT BAY. b, MAXILLA. 



Cj MANDIBLE OF A PARATYPE. 



an underlying cellular or spongy layer in some specimens. It clings 

 rather firmly to the walls. 



Height 16 mm.; rostrocarinal diameter of base 12 mm., lateral 

 diameter 11.5 mm. ; rostrocarinal length of orifice, 10 mm. Height 

 12 mm. ; rostrocarinal diameter 11.5, lateral diameter 12 mm. ; rostro- 

 carinal length of aperture 8.5 mm. 



The labrum (fig. 37) has a finely hairy edge with two small teeth 

 on each side. There are no hairy tracts on its lateral faces. 



The mandibles (fig. 37<?) have three rather slender teeth and a 

 blunt or divided fourth one partly united with the lower point. The 

 maxillre (fig. 376) have two strong spines above, the margin notched 

 below them, then becoming convex, the lower angle being broadly 

 rounded. The edge bears about 10 spines, the lower ones stronger, 

 and there is a tuft of fine bristles below the lower extremity. 



The first pair of cirri has very unequal rami, the anterior branch 

 of about 23 segments, and about twice the length of the shorter 

 ramus, of 11 segments, which are strongly protuberant on the for- 

 ward side. Another individual has 21 and 12 segments in the rami 

 of the first cirrus. The second pnir of cirri has rami of 13 and 12 



