56 



BULLETIN" 93, UISTITED STATES NATIONAL MUSEUM. 



ridged, the ridges near the base shghtly crenulated by longitudinal 

 strise, which are very fine or subobsolete in the intervals. The 

 articular ridge is high, flattened and reflexed, not much more than 

 haK the length of the tergal margin, its lower end usually overhanging. 

 Adductor ridge confluent with the articular above, continued down- 

 wards in a broad, rounded callous ridge or merely a general tliicken- 

 ing of the median part of the valve, boimding the depressor muscle 

 scar. Muscle impressions deep; occludent edge folded over near 

 the base. 



Tlie tergum (pi. 10, figs, la, Ih) is purplish toward the apex, 

 triangular, broad, dehcately ridged, with the groove to the spur 

 closed, Tlie spur is long, and separated hy about twice its width from 

 the hasiscutal angle. The articular ridge and the reflection of the 

 scutal edge are both high and acute. The external ridges denticulate 

 the scutal border. 



ElG. 9.— BALANUS TINTINNABULUII. a, MIDDLE SEGMENT OF CIIiEUS VI. 6, MANDIBLE. C, MAXILLA. 



d, LABEUM. 



Comfartmeyds. — Tlie radii are wide, with level summits. The outer 

 lamina of the wall bears numerous short lamellae on its inner edge 

 (pi. 10, fig. le) between the septa. The parietal tubes are entirely 

 open, except quite near the summits, wheio they have numerous 

 transverse septa. The interlocking septa of the radii and sutural 

 edges are straight, regular, and denticulate on both sides. 



The labi-um has a straight, shortly hairy edge and narrow notch. 

 In the specimen examined there are two small teeth on one side, one 

 on the other (fig. 9d). 



The mandible has four strong teeth, the fifth tooth small, united 

 with the blunt lower pomt (fig. 96). 



The maxilla has a straight edge and 14 large spines; those below 

 the upper large pair are in two series (fig. 9c). 



The cirri i to iii are shorter than in other groups of the genus. 

 Cirrus i has rami about 5 mm. long, of 17 and 15 segments, those of 



