384 
PALEONTOLOGY: J. M. CLARKE 
shows the carapace of the crustacean just before attachment with the head 
portion and the dorsal side downward — a rather natural position for phyllo- 
pods, which, like Apus, are wont to swim on their backs, while foraging along 
the bottom. 
The head and back being thus protected by attachment, but the ventral 
side open to attack, the next step will be the separation of the carapace valves 
along the hinge line and their movement upward towards the ventral side; 
and likewise the rostral and dorsal plates will have to move upward to fit in 
again between the valves (stage II of diagrams). Following this was the 
breaking up of the valves into the lateralia, owing to stresses exerted at one 
or other end, possibly the anterior one where the originally chitinous and some- 
what flexible valve was attached. Here also, our material affords a clue to the 
mode of procedure. A very early growth stage of Eobalanus shows four 
radially arranged, subequal, oval plates, the two lateral ones of which show 
a suture along which a smaller part is being split off. It is thus to be inferred 
that the compartments were formed by successive splitting off of plates from 
the original valve, each fissure producing a new pair of lateralia. In this way 
the peculiar interlocking arrangement of the compartments in Eobalanus 
would finally have come about and each valve of the carapace have been 
divided up without leaving a useless remainder. 
The scuta and terga which form the valvular carapace or operculum of the 
upper aperture of the later Balanidae and Lepadidae and which are of great 
taxonomic importance, have not been found in Eobalanus and Protobalanus, 
and in our view did not exist then, but are a later development to close in 
more completely the ventral side. They are not fundamental structures. 
POSSIBLE DERIVATION OF THE LEPADID BARNACLES FROM 
THE PHYLLOPODS 
By John M. Clarke 
State Museum, Albany, N. Y. , 
Communicated, October 29, 1918. 
Mr. Ruedemann's discovery of an elemental balanid and his constructive 
deduction therefrom of the origin of the acorn barnacles, sets this form of 
symbiotic degeneration back to an historic stage, where its phylogeny is in- 
dicated in its own structure. The degeneration is already complete and hence 
implies a long time for the acquirement of such adaptation, but it is also so 
simple as to indicate its procedure. If Eobalanus intimates the rise of the 
Balanidae through the decline and dependence of the Phyllopods, it is oppor- 
tune to regard the evidence bearing on the phylogeny of the other great * 
division of the barnacles, the Lepadidae or Goose Barnacles. 
