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PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol. 59. 



The tergum (fig. la) is thin, flat, having fine, transverse riblets and 

 some weak radial striae. The short, obliquely truncate spur is fully 

 half the basal width of the valve. 



The compartments are very firmly united. The parieties have no 

 tubes. The walls are thick, very deeply furrowed between the high 

 ribs, which are unequal, two on each side usually being flat-topped, 

 with narrow raised borders. The radii are narrow, not readily dis- 

 tinguishable. Internally there is a short sheath, overhanging deep 

 cavities; the compartments below it coarsely folded like a heavy 

 drapery and toward the base closely costate. 



The basis is calcareous, solid, radially grooved inside. 



The labrum, mandible, and maxillae (fig. 2a, 5, c) are substan- 

 tially as in Balanus hesperius. The palpi are also similar, but less 

 profusely bristly. 



Fig. 2. — Balanus engbeegi. a, Labrum ; b, maxilla ; and c, mandible. 



The first cirrus has very unequal rami ; the shorter, of 8 protuber- 

 ant segments, a little more than one-third as long as the longer, which 

 consists of at least 21 segments. Cirrus II has rami not very unequal, 

 about 2 segments of the longer projecting beyond the shorter. In 

 cirrus III the rami are equal. The posterior cirri have four pairs 

 of spines on the segments, the lower pair very small. There are long 

 posterior-distal spines, as in Balanus hesperius. 



On the third cirrus there are a few excessively minute multifid 

 scales distally on some segments, such as have been figured for 

 B. crenatus curviscutum (Bull. 93, fig. 55a), but vertically placed, 

 and not accompanied by small spinules. 



Comparisons. — While this species is evidently related to Balanus 

 hesperius, it differs conspicuously by the far wider spur of the tergum 

 and by the distinct longitudinal striae of the scutum, which is plain 

 inside. Externally it differs by the very strong ribs of the wall ; but 

 this is not usually a character of much constancy. Balanus glandula 

 Darwin is most easily differentiated by its scutum, pitted below the 



