6 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 125 
Although there are notable differences in the coloration of these 
two species, by far the greatest number of distinguishing characters 
are found in the opercular plates. The scutum of the Caribbean 
species is about one-half as tall as it is wide, whereas in C. stellatus 
it is about two-thirds. In the latter species the adductor muscle pit 
is exceedingly large and the basal end of the articular ridge is acute, 
extending out to the basitergal angle; the opposite conditions exist 
in C. angustitergum. In C. angustitergum, furthermore, the tergum is 
narrow—hence, the name—the width being about one-half the 
height and the spur being well set off from the basiscutal angle, 
but in C. stellatus the spur is virtually confluent with the basiscutal 
angle and the height of the plate exceeds the width by one-fourth or 
less. Crests for the tergal depressor muscles, of which there are four 
in CO. stellatus, are low and feebly developed. In C. angustitergum 
there are five crests, which are both high and strongly developed. 
Insular populations of C. angustitergum in the Caribbean are 
obviously isolated geographically from the Asia Minor, Mediter- 
ranean, and eastern Atlantic populations of C. stellatus—indeed, 
there is no indication of recruitment of C. stellatus in the Caribbean; 
consequently, the populations of these two species are reproductively 
isolated and more than likely have been for a significantly long 
period. Such isolation, both reproductive and spatial, speaks in 
favor of eliminating the antequated subspecific label attached to 
C. angustitergum. 
There are at least three other species of Chthamalus in the Caribbean 
and western Atlantic: C. fragilis Darwin, 1854; C. stellatus thompsont 
Henry, 1958; and ©. rhizophorae de Oliveira, 1940. There should be 
little confusion regarding the identity and distinction among these 
species. Ohthamalus fragilis is confined for the most part to the 
Atlantic coast of the United States, although it has been reported 
in the Caribbean and on the west African coast (Stubbings, 1967, 
p- 262). Bermuda is apparently the only locality where C. stellatus 
thompsoni occurs (Henry, 1958, p. 220). The euraphian, C. rhizophorae, 
has been collected by the present writer at several localities in the 
Bahamas, although previously it was known only from Brazil 
(Oliveira, 1940b, p. 379; Stubbings, 1967, p. 257). 
Family TETRAcLITIDAE Nilsson-Cantell, new status 
TerRacLitina® Nilsson-Cantell, 1921, p. 357. 
At the present time, students of balanomorph systematics favor 
inclusion of the tetraclitids in the family Balanidae. Although Nilsson- 
Cantell (1921) took the first and only bold step when he segregated 
the two dozen or so species of this complex into a distinct subfamily, 
