A REMARKABLE ORUSTACEAN PARASITE. 115 
degradation. No head region is distinctly marked off as such, 
only one pair of mouth appendages is recognisable, the thoracic 
appendages are reduced to a far simpler character, the abdominal 
region has almost disappeared, and segmentation occurs only in 
the posterior region of the body. 
On the other hand, the resemblances that exist between the 
two forms are so marked that it is impossible to doubt of a 
close genetic relationship. The similar habit of parasitism 
upon Anthozoa, the presence of a large lateral carapace into 
which penetrate the organs of digestion and of reproduction, 
the similar construction and dorsal flexure of the antenne, 
the presence of six pairs of thoracic appendages and of a more 
or less reduced abdomen, the hermaphroditism (a rare feature 
among Crustacea), are ordinal characteristics of these two 
animals and of Synagoga, and are found in no other single 
group. We may unite them under the name Ascothoracida, 
suggested by Lacaze-Duthiers, and accepted by Norman in his 
account of Synagoga. 
The main differences between Laura and Petrarca, in addition 
to those mentioned above as being indicative of a further 
degradation, are: (1) the extension of the carapace over a 
larger number of segments in Petrarca; (2) the development by 
the latter of two additional median ceca on the intestine; and 
(3) the position of the testes. With regard to this latter point, 
it is interesting to note that while in Petrarca the testes are in 
the thorax, and in Laura at the bases of certain of the limbs, 
they occur in (adult) Cirrhipeds in both regions, lying above 
the nerve-cord and filling the protopodite of the first five and 
sometimes also of the sixth pairs of legs. 
RELATION OF THE ASCOTHORACIDA TO THE CIRRHIPEDIA AND 
OstTRACODA. 
It was stated above that the characteristics of the Ascothor- 
acida are found in no other single group, but they are so 
markedly shared between the Cirrhipedia and Ostracoda as to 
suggest that they may indicate a genetic relationship between 
