REPORD OF THE, DIRECTOR, 1922 93 
AN ANCESTRAL ACORN BARNACLE 
By Rupo_tF RUEDEMANN 
While studying Utica and Lorraine fossils of New York, the 
writer discovered elliptic bodies attached to shells of Geisonoceras, 
that are composed of 12 triangular plates, which at once suggested 
their reference to the acorn barnacles. A brief preliminary paper 
on “ The Phylogeny of the Acorn Barnacles ” was published in 1918 
in the Proceedings of the National Academy of Sciences (vol. 4, 
pp. 382-386, 1918),’ and the suggestion made that the fossils, for 
which the new generic term Eobalanus is proposed, indicate 
by the inverted form of the middle lateralia (see text, fig. 1, figs. 
V & VI) the origin of the two series of 5 lateralia from the two 
valves of a phyllocarid, such as Rhinocaris, and a progressive devel- 
opment from Eobalanus through the Devonian Protobalanus and 
the later Catophragmus into Balanus is suggested as shown in the 
diagram. 
It was intended to publish the full account with figures in a mono- 
graph of the Utica and Lorraine formations of New York. This 
manuscript, however, has now been ready for the printer for four 
years and there is no immediate prospect of the paleontologic part 
being published. Meanwhile the preliminary note has called forth 
from several students of crustaceans expressions of doubt and 
requests, both in print and in letters, for the full facts in the case. 
To satisfy this natural curiosity we publish herewith the chapter on 
Eobalanus from the manuscript of the monograph. 
To the species of Eobalanus originally discovered on cephalopods 
of the Utica shale, meanwhile another has been added that was 
found on a cephalopod from the Trenton limestone. This also is 
here described. We have no doubt that careful search of the 
Ordovician cephalopods in other countries will bring to light still 
more species of this highly interesting barnacle, and possibly add im- 
portant facts on the development of the barnacles, the most mysteri- 
ous of all crustaceans. 
Genus Eobalanus nov. 
Shell composed of 12 mural compartments, viz: 10 lateralia, the 
carina and the rostrum. Of the 2 series of 5 subtriangular lateralia 
_ Followed by a note by John M. Clarke on the phylogeny of the Lepadidae, 
in which is pointed out that the Ordovician Lepidocoleus may indicate a simi- 
lar path of derivation of the Lepadidae from the phyllopods. 
