522 Reviews—The Structure of Trilobites. 
two years ago (Grou. Maa., 1919, pp. 359-63), and a comparison 
of the conclusions reached by the two writers is of particular 
interest. Their substantial agreement on all the main points of 
structure is of importance as showing that our knowledge of the 
Trilobites’ appendages rests upona sure basis. It is only on matters 
of detail that there is difference of opinion. 
The author has been unable to convince himself of the presence 
of the epipodites and exites described in Neoleaus and some other 
genera by Walcott, and he considers that the appendages were in 
all cases simply biramous. The two branches are connected with 
a single basal segment produced inwards to form a gnathobase, 
or, as Raymond prefers to call it, “ endobase.” Walcott described 
this basal segment as formed by the fusion of two segments, the 
coxopodite and basipodite. Raymond regards it as representing 
the coxopodite alone, the second free segment being the hasipodite, 
and he states that the exopodite articulates with both of these 
segments. At the point of attachment of each coxopodite with the 
body is a calcareous process extending “down from the dorsal 
test just inside the line of the dorsal furrow ”’. These processes are 
designated “ appendifers ”, and are compared with the entopophyses 
of Limulus. 
In his recent monograph Walcott adheres to his interpretation of 
the sections of Calymene, Ceraurus, and Acidaspis as showing that 
these genera possessed spirally coiled branchiz. Raymond discusses 
at length the evidence for the existence of these remarkable 
structures, and while admitting the difficulty of interpreting the 
appearances seen in the sections, he comes to the conclusion that the 
appendages in these genera did not differ in essential structure from 
those of other Trilobites in which the limbs are exposed on the surface 
of the fossils. 
On the question of the affinities of the Trilobita, Raymond is In 
agreement with Walcott in regarding them as most nearly related 
to the Crustacea. He even includes them within the sub-class, and 
regards the other groups of Crustacea as derived directly from 
Trilobites. In taking this view he has, perhaps, hardly allowed due 
weight to the non- -crustacean characters alluded to in the review 
already quoted (Grou. Mac., 1919, p. 563). He also considers it 
possible that all the other groups of Arthropoda may yet be traced 
back to a Trilobite ancestry, but he is careful to point out the wide 
gaps that remain to be filled in before this can be done. 
Many criticisms might be offered on points of detail. For example, 
he states that “ the exact homology, segment for segment, between 
the walking legs of the trilobite and those of many of the 
‘Malacostraca, even the Decapoda, is a striking instance of retention 
of primitive characteristics in a specialized group”. This exact 
homology, hewever, is only obtained by assuming that the ex <opodite 
articulates with both the coxopodite and the basipodite, an arrange- 
ment not found in any Malacostracan, nor, indeed. in any Crustacean. 
