THE SESSILE BAEl^ACLES. 193 



The sin^^'le west American s])ecies composing this <^roiip resembles 

 Solid oh alctnus in the hard parts, but has the mandibles and maxilhe 

 formed as in the typical Balami^, and unlike those of any poreless 

 group of the genus. It is possible that we have to do with a second- 

 arily simplified group descended from some ancestor of the B. cre- 

 natus stock. At all events, Hesperihalanus is not at all closely re- 

 lated to SoUdohalanus, Arnmtohalanus^ Chirona, or any other poreless 

 subgenus. 



BALANUS HESPERIUS, new species. 



Plate 49, figs. 1-ld, l-lh, 8. 



Type.— Cat No. 32935, U.S.N.M., from Albatross Station 3483. 



Dlstr'thution. — Alaska, Bering Sea. 



The barnacle is small, conic or shortly cylindric, white or buff, 

 typically ribbed in the adult stage, but sometimes smooth ; epidermis 

 very thin, pale yellow, usually fugacious. 



Greatest basal diameter of type 15.7 mm.; height, 7.2 mm. The 

 largest specimen seen is from Attn, Aleutians, measuring 22 mm. in 

 greatest diameter ; the longest compartment 17 mm. high. The ordi- 

 nary size is 12 to 16 mm. diameter. 



The scutum (pi. 19, figs. 16, Ic, Id,) is shaped like that of B. 

 crenatus; tergal border slightly inflected, longer than the basal; the 

 occludent border often slightly convex, thick. Sculpture of close, 

 sharp growth-ridges, every alternate one more prolonged and higher 

 on the occludent edge ; over the ridges there is a very minute longi- 

 tudinal striation. The articular ridge is very high, reflexed, and 

 usually ends in a point ; adductor ridge very short, passing upward 

 into a heavy callus between the articular ridge and the deep pit of 

 the adductor muscle, this callus hclng cut into several sharp ridges^ 

 which typically terminate downward in teeth. Articular furrow 

 deep. Pit for the lateral depressor muscles very small but sunken. 



The tergum (pi. 49, fig. la) has a rather short carinal margin. 

 Articular ridge well developed, triangularly overhanging the upper 

 part of the broad articular furrow. Spur short, one-fourth the width 

 of the valve or less, rounded or subtruncate, and standing very close 

 to the hasiscutal angle. The external face is flat, with a very slight 

 depression running to the spur. Growth-ridges delicate, mainly 

 epidermal, stronger on the scutal side. There are some weak radial 

 striae near the carinal margin. 



CoTYhpartments. — The parietes have no pores or tubes whatever. 

 Their inner faces are very strongly and deeply ribbed, the ribs more 

 or less crenulated at the base, and generally unequal. The sheath 

 is extremely short, the opercular valves, therefore, lodged high in the 

 orifice. liadii broad/ their summits making angles of about 45° with 



