A REMARKABLE ORUSTACEAN PARASITE. 107 
A Remarkable Crustacean Parasite, and its 
Bearing on the Phylogeny of the Ento- 
mostraca, 
By 
G, Herbert Fowler, B.A., Ph.D., 
Assistant to the Jodrell Professor of Zoology, University College, London 
With Plate VIII. 
In a decalcified specimen of Bathyactis symmetrica, 
dredged on the expedition of H.M.S. “ Challenger” from a 
depth of 2300 fathoms (Lat. 35°41’ N., Long. 157°42’ E., 
Station 241), I was fortunate enough to meet with the re- 
markable parasite for which I propose the name of Petrarca 
bathyactidis, gen. et sp. n. Its morphological interest, and 
the improbability that further material will be obtained for 
some time, are justification sufficient for the presentation of 
an account which is unavoidably incomplete, owing to the 
minuteness of the animal and to the fact that only three 
specimens have been at my disposal. 
Petrarca is a member of that curious family of Crustaceans, 
of which the Laura gerardiz of Lacaze-Duthiers (‘ Mém. 
Ac. Sci. Inst. France,’ xlii, 1883), and the Synagoga mira of 
Norman (‘ Rep. Brit. Assoc.,’ 1887, p. 86), are the only other 
examples, a family of parasites or semi-parasites upon Anthozoa, 
generally regarded as forming a part of the class Cirrhipedia. 
To the question of the zoological position, reference will be 
made after a description of so much of the anatomy as it has 
been possible to discover. 
As to its occurrence, the specimens were all found in the 
mesenterial chambers of a single Bathyactis; their presence 
