90 
Fig. 3. Mouthparts of A. clippertoni (Schmitt) and 
A. paragracilis Coutiere. a, b, Mandible and third 
maxilliped of A. clippertoni; c, d, mandibles from 
third maxilliped of A. paragracilis . 
PACIFIC SCIENCE, VoL XVIII, January 1964 
fifth walking legs. In Pomognathm there are 
"no epipods on any thoracic legs.” 
A group of 60 specimens of A. paragracilis 
from much of the range represented in the 
collections (Society, Cook, Samoa, Tonga, Ha- 
waii, and Marshall islands) were examined; of 
these 58 lacked the last mastigobranch and 
setobranch normal for Alphem, with the final 
epipodites occurring on the third and fourth 
walking legs. One had a rudimentary mastigo- 
branch on the fourth, with no setobranch on 
the fifth, therefore approaching the condition 
normal to Alpheus; and the last lacked the mas- 
tigobranch on the third leg, approaching the 
condition of Pomognathm. In 30 specimens of 
A. clippertoni from a similar geographic range 
all specimens were like the normal A. paragra- 
cilis, with the last mastigobranch on the third 
and the last setogranch on the fourth. The ques- 
tion is, how much reliance should be placed on 
the branchial formula as an absolute generic 
criterion? Certainly the formula is not fixed in 
A. paragracilis, nor is it constant in other genera 
(see Banner and Banner, 1960:134). 
To us it appears that Pomognathm corallinus 
is an extension of the line of modification found 
in A. paragracilis and A. clippertoni , both in 
structure of the mouthparts and ha branchial 
formula. Pomognathm does not show close re- 
lationship, in our opinion, to Synalpheus , and 
the reductions of the epipodites in Pomognathm 
is merely parallel to that of Synalpheus . It is 
possible that additional species may be found 
intermediate between A. paragracilis and P. 
corallinus; if they are found, the whole series 
should be reconsidered. However, for the present 
we believe that the A . paragracilis and A . clip- 
pertoni should be retained in Alpheus , and Po- 
mognathus should be considered as a distinct 
genus. 
Alphem macro chirm Richters 
Alphem macro chirm Richters, 1880. Meeres- 
fauna der Insel Mauritius und der Seychel- 
len, Decapoda, p. 164, pi. 17, figs. 31-33. 
Nec Alphem macro chirm de Man, 1888. 
Arch, fur Naturgesch. 53(1) : 5 19= 
LOCALITIES: Canton Island: 1 specimen from 
BC 14; 1, BC 16. Christmas Island: 5 specimens. 
