NOTES ON A SPECIES OF BARNACLE. 
403 
days in a flat dish molted twice and at the end seemed quite healthy. The water 
was changed six times. 
Those crabs whose gills are heavily burdened with Dichelaspis have less vitality; 
their movements are sluggish and they are the lirst to die when brought into the 
laboratory. This reduction of vitality is not an evidence of real parasitism, but may 
be explained by the fact that when the cirripeds are present in large numbers much 
of the gill surface is occupied, gill lamellae are fastened together, and the respiratory 
current retarded by them, and the barnacles have the first chance at the water. The 
health of the host being thus impaired, much harm results indirectly to it, in that it 
is rendered less able to contend with its enemies or to escape their attacks. 
The following is an explanation of terms used in the description: 
The capitulum incloses the body, and is supported upon the stalk or 'peduncle. 
The juncture of the capitulum with the peduncle is regarded as the base of the capitulum; the 
angle opposite this juncture is the apex. 
Upper means away from; lower toward the base. 
The rostral angle or umbone is indicated by the point of union of the two segments of the scutum. 
The occludent margin of the capitulum extends from the rostral angle to the apex. 
All of the carina, except its basal portion, takes part in the carinal margin, which is thus approxi- 
mately at right angles to the base. A tergum, therefore, has, roughly, four sides — upper, carinal, 
lower, and occludent. 
The term plates or valves ( terga , scuta, carina) applies to the calcified portions of the valves. 
DESCRIPTION. 
Darwin (1851-1854) gives this diagnosis of the genus Dichelaspis : 
Valves 5, generally appearing like 7, from each scutum, being divided into two distinct segments, 
united at the rostral angle; carina generally extending up between the terga, terminating downward 
in an embedded disk or fork or cup. Mandible, with three or four teeth; maxillae notched, with the 
lower part of the edge generally not prominent; anterior ramus of the second cirrus not thicker than 
the posterior ramus, nor very thickly clothed with spines; caudal appendages uniarticulate, spinose. 
As will be seen from the description given below, the cirriped under considera- 
tion belongs to this genus. While the carina, which terminates downward in a fork, 
usually reaches only to or barely beyond the lower edges of the terga, there is con 
siderable variation in the size and shape of the plates. To this barnacle I have given 
the name Dichelaspis mutter i. * After a description of the species there will follow 
a comparison of D. mulleri with other species of the same genus. 
Dichelaspis mulleri. 
Capitulum barely longer than broad; basal segment of scutum parallel to lower margin of 
capitulum, narrower than occludent segment and about five-sixths as long; tergum divided very 
unequally by a notch; lower part of tergum about twice as wide as occludent segment of scutum; 
carina terminating downward in a fork; mandible with four teeth. 
The capitulum is less than 1 j> times as long as broad (fig. 2), generally about half as thick as long, 
sometimes more compressed. In two of the largest specimens the capitula were 3 mm in width by 
in length. Others of a much more usual shape were 3 nmi by 3$ mm . These were unusually large. 
The peduncle is 1 f to 3 times as long as the capitulum, but one specimen was found with a capit- 
ulum 4 mm in length and peduncle 40 mm in length. The peduncle is translucent, except when colored 
by the ova, which, when present, give to a greater or less portion of the peduncle a pink color. 
* Named after Fritz Muller, who says in his “ Facts and Arguments for Darwin ” (English translation, 1869, p. 137) that 
he has met with a species of Dichelaspis m the branchial cavity of Lupa dicantha ( Callinecles hastatus formerly included 
under this name) He does not describe the form, which may well be identical with the Beaufort species. 
