402 CONTRIBUTIONS TO MARINE BIONOMICS. 
III, The Systematic Features, Habits, and Respiratory 
Phenomena of Portumnus nasutus (Latreille). 
The crab whose habits I now describe has not previously been 
recorded as an inhabitant of British seas. I found two specimens, 
both male, imbedded in a patch of coarse shell sand on the south side 
of Drake’s Island at low water, spring tides: one on August 11th, 1896, 
and the other on the following day. 
1. NOMENCLATURE. 
My first impression on noticing this remarkable little crab 
was that I had an abnormal specimen of a young Carcinus maenas 
before me; but the possibility of such a leap from the normal as the 
frontal area of this specimen would produce on a variation-chart 
was soon disposed of by Professor Weldon, and we identified the crab 
with the Portunus biguttatus of Risso (1816), now usually known under 
the name Platyonichus nasutus of Latreille (1825, p. 151; ef. also 
Milne-Edwards, 1834; Costa, 1853, p. 11; Carus, 1885). 
The genus Platyonichus of Latreille (1818) was originally coextensive 
with the genus Portumnus of Leach (1815), Latreille having simply 
altered Leach’s name owing to its similarity to the name Portunus, 
with which he feared it might be confused. Dana (1852), however, 
and Bell (1853), showed that the species included within the genus 
Platyonichus were separable into two well-marked groups, which were 
accordingly named by these writers Platyonichus and Portumnus 
respectively, the latter name being reapplied to the group which 
included Leach’s type, viz. Portumnus latyes. It is to the latter 
group that Platyonichus nasutus belongs, so that I must refer to it 
for the future as Portumnus nasutus. 
It is true that the earliest specific name applied to the present species 
is biguttatus of Risso (1816), the name nasutus of Latreille (1825) being 
nearly ten years later. Since, however, the species has been invariably 
referred to under Latreille’s name, probably owing to the influence of 
Milne-Edwards’ adoption of it, I submit that we have here an ex- 
ceptional case which demands exceptional treatment. The rule of 
priority provides a decisive method of dealing with a confused and 
complicated synonymy; but its application in the present case could 
not be urged on such grounds, and would be distinctly inconvenient. 
I shall therefore adhere to the employment of Latreille’s name nasutus 
in referring to the species under discussion. In the event, however, 
of possible differences being discovered between Mediterranean and 
Atlantic races of this species, I would point out that Risso’s name 
