32 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



myophore, concave on its upper face, and situated rather high on 

 the plate. 



The fixed tergum is a subquadrate plate with the four angles pro- 

 duced. Its surface is divided into four triangles by lines from the 

 corners to the acute, recurved, but scarcely projecting apex. (1) The 

 largest triangle has the basal margin as its base, and is without 

 special sculpture; (2) a small, radially ribbed and concentrically 

 striate aliform triangle toward the fixed scutum; (3) a lineolate 

 triangle between the apices of the two terga; and (4) a long triangle 

 extending between the carina and the movable tergum. The interior 

 of this plate is rather heavily calloused in the middle, but less than 

 in F. stromia. 



Greatest carinorostral length 7.5 mm.; length between apices 6 

 mm.; greatest breadth, at right angles to preceding, 7 mm.; height 

 from base to summit of the movable scutum 4 mm. 



Other individuals measure: 5, 3.7, 4.8, 2 mm., and 7, 5.6, 6.8, 

 3 mm. 



This species is related to F. alba Pilsbry, but it differs by the sculp- 

 ture of the movable plates by the internal structure of the fixed 

 scutum, and by lacking short, arcuate ribs above the upper articu- 

 lating rib of the carina. F. alba is smaller, so far as known, and since 

 all the individuals seen sit upon narrow echinid spines, the contour is 

 different. 



The general shape of the plates of the wall varies among the speci- 

 mens, being dependent upon the irregularities of the supporting 

 surface. Most of them have spreading walls, as in that selected 

 as type (figs. 1-lc), but in some examples, hampered by a restricted 

 base of support, the walls become steep, the tergo-scutal wall vertical 

 or overhanging. Such an individual is drawn in figure 3. It grew 

 upon a rather small Dorocidaris spine, the rostrocarinal axis of the 

 barnacle transverse to the spine, and the base in consequence deeply 

 concave. The .greatest rostrocarinal length of this individual is 

 5 mm. 



This species has been somewhat fully figured in order to show the 

 amount and kind of variation to be found among individuals of one 

 colony, brought up in one haul of the dredge. The lot, consisting of 

 15 individuals, was taken by Mr. John B. Henderson, jr., during the 

 1911 cruise of the yacht Eolis. 



Cirrus i has rami of 14 and 11 segments, the shorter ramus three- 

 fifths the length of longer. In cirrus ii the shorter ramus is over 

 two-thirds the length of the longer, the other cirri having subequal 

 rami. The terminal appendage has 23 joints, is more than three 

 tunes the length of the protopod, decidedly over half the length of 

 cirrus vi. 



The penis is very stout, about twice as long as the protopod, sparsely 

 hairy near the end, as usual. 



