692 L. A. BORRADAILE. 
(12) The third masilliped with the exopodite shorter than the endopodite, carrying a straight, 
jointed flagellum directed forwards, and the endopodite narrow, with separate ischiopodite and 
meropodite. 
(13) All the Jegs seven-jointed. The first three pairs chelate with normal chelae, the first 
the greatest, equal, the fourth pair simple, the fifth pair simple (?) and having its last two joints 
slightly twisted so that, when the basal joints are pressed against the sides of the body, while 
the last joint of the fourth pair points downwards and backwards, that of the fifth pair points 
forwards and inwards’. 
(14) The gills many, including mastigobranchs and podobranchs on all the thoracic limbs but 
the last, arthrobranchs on all but the first and last, and pleurobranchs on the last four. 
(15) The thoracic segments which bear the legs with distinct sterna, which are not very broad, 
but grow broader from before backwards, and are all fused except the last”. 
(16) The first pair of abdominal limbs unbranched. Those of the second to fifth segments 
with two fairly broad branches, the inner of which bears an appendix interna (Fig. 126c). The last 
pair about as long as the telson, with broadly oval branches, across the outer of which is a suture. 
The internal anatomy of the various groups is not yet well enough known to allow of general 
statements being made about it. 
The animal was hatched in the Zoea stage, with a segmented abdomen but no limbs behind 
the third maxilliped, and passed through a Mysis stage with exopodites on all the legs. 
The descendants of the crustacean which we have thus reconstructed fall into two 
sets, one comprising the Eryonidea, Scyllaridea, and Nephropsidea, in which the abdomen 
is strong and well-armoured, stretched out unprotected, and used as a swimming organ by 
means of its tail-fin, and the other containing the rest of the groups, in which it has for 
some reason become a burden and a source of danger to be protected and kept from 
exposure, even though it be still shaped and used for swimming. The first of these sets 
is on a lower and more primitive grade of organisation than the second. This is shown 
(1) by the abdomen, with its stout armour, overlapping terga and pleura, strong processes 
to clip the carapace on the first segment, broad tail-fin, and, in the Eryonidea and Scyllaridea, 
appendices internae. To this form of abdomen, which is always carried at length, I shall 
restrict the term “macrurous.” (2) by the legs, which in the Eryonidea and Nephropsidea 
are chelate in the first three pairs and have seven joints (except for the first pair of the 
Nephropsidea) whereas in all other Reptantia they have only six, owing to the fusion of 
the basipodite and ischiopodite, (3) by the large number of the gills, (4) by the slender 
third maxillipeds with their long flagella directed forwards, (5) by the broad antennal scale of 
the Eryonidea and Nephropsidea. Of course some of the foregoing characters are found in 
primitive members of other groups, but they stamp this set of groups as a whole. Of the 
three macrurous groups, the Eryonidea and Scyllaridea are more nearly allied together than 
either of them is to the Nephropsidea. They have both lost, or much reduced, their rostrum 
(except Palinurellus), reduced the inner lobes of the second maxilla, and fused their carapace 
at the sides with the epistome, but they have kept the appendices internae. Their body 
1 This character, though it is most prominent in the but also in the Thalassinidea, Potamobiidae and Parastacidae 
Anomala and Thalassinidea and the lower Crabs, is seen to and in the prawn Stenopus. In Penaeus the anterior sterna 
some extent even in the more primitive groups, as the are free, but the last two are joined by secondary thickenings 
Palinuridae and Potamobiidae. in the membrane between them. 
2 A primitive feature, found not only in Boas’ Anomala 
