244 BULLETIN 93^ UNITED STATES NATIONAL MUSEUM, 



ACASTA CYATHUS Darwin. 

 Plate 57, figs. 1-3. 



1854. Acasta cyathus Darwin, Monograph, p. 312, pi. 9, figs. 3rt-3c. 



1906. Acasta ryathus Darwin, Annandale, Supplementary Keport No. 31, 



on the Cirripedia, in Herdman's Rep. Pearl Oyster Fisheries of the 



Gulf of Manaar, p. 144. 



Distribution. — Madeira; West Indies, west coast of Florida, and 

 near Colon. 



Darwin's description of this species is as follows : 



Carinolateral parietes about one-fourth of width of lateral parietes ; radii 

 wider than the parietes; basis nearly flat, small; tergum with the spur trun- 

 cated, half as wide as valve. 



General appearance. — Color pale pink, or that of flesh ; basis remarkably flat 

 and rather small, with the walls above bulging out a little. The radii are very 

 wide, being wider than the parietes to which they belong; the orifice is gener- 

 ally rather large. The parietes of the carinolateral compartments vary from 

 one-third to one-fourth of the width of the parietes of the lateral compart- 

 ments. Basal diameter of largest specimen .35 of an inch. Internally, the 

 parietes are generally more strongly ribbed than .4. sponr/ites. 



The opercular valves are large, owing to the form of the shell. The scuta 

 present no particular character, and are not distinguishable from those of A. 

 sulcata, but the adductor ridge is perhaps rather more developed. The terga 

 [pi. 57, figs. 1&, 2a] are nearly as large as the scuta, and this is an unusual cir- 

 cumstance; the spur is more than half as wide as the valve; it is placed not 

 quite close to the basiscutal angle ; on the carinal side the basal margin of the 

 valve slopes a little toward the spur. I may mention that in several specimens 

 from IMadeira the scuta and terga, on one side, had grown to a monstrous 

 thickness. 



Cirri : These resemble in every respect those of A. sponrjites, with the remark- 

 able exception that on the anterior ramus of the fourth cirrus several segments 

 were furnished with the beautiful downward curved mandiblelike teeth, as in 

 A. sulcata; but differently from in that species, there were none on the upper 

 segment of the pedicel. I should have thought this an excellent specific char- 

 acter had not these teeth Been so extremely variable In .4. sulcata. 



Two American specimens which I dissected show considerable varia- 

 tion in the armature of the cirri ; one from near Colon (pi. 57, figs. 1 

 to Ih; text figs. 79, 80« to 80^), the other (pi. 57, fig. 3; text figs. SOe 

 to 80A), from near the Dry Tortugas, Florida. 



The labnim has two teeth on one side of the median notch, none on 

 the other (fig. 79«.). 



The mandible has four teeth and a truncated or denticulate lower 

 point (fig. 7dh). 



Maxilla has a straight edge, armed Avith 10 spines below the upper 

 great pair, three near the lower angle are larger than the others. 

 There is a tuft of small, short spines below the lower large one 

 (fig.79e). 



The first cirri have slender rami of 17 and 9 segments, the anterior 

 ramus nearly double the length of the posterior. 



