500 J2B. KEYS. 
deep in the shingle. Rame Head, April, 1902, three examples. 
Shaldon, one, de la Garde. Torcross, August-September, 1907, 
G. C. Champion. Side of the Exe, rare, Parfitt. 
{CILLENUS LATERALIS Sam. Millbrook Creek and mouth of the Yealm, 
in numbers. Wivelscombe Creek and Bere Ferrers, a few specimens. 
Dawlish Warren, one example, February, 1908, de la Garde. 
{TacHys PARVULUS Dej. Four specimens, in shingle just below high 
water, about half a mile beyond Bovisand, June, 1905. 
tALPUS MARINUS Strém. Generally distributed all along the coast from 
the Yealm to Cremyll, also found in the estuaries at Wivelscombe, 
Bere Ferrers, etc. Some seasons abundant. At Batten, October, 
1909, quite 200 under one boulder, 70 were captured. Once only I 
found them in numbers in the roll of rejected seaweed at high-water 
mark at Millbrook Creek, their usual habitat being under stones 
embedded an inch or two in clayey shores. They occur practically all 
the year round and their larve may often be taken with them. In 
1888 the insect could be obtained at Tinside and in coves between 
the rocks under the Citadel. Shaldon, de la Garde and G. C. Cham- 
pion, August-September, 1907. 
tA. Rosin Laboulb. This species is very like the preceding, but, besides 
its well-known specific differences, is of more robust build. It occurs 
all along the coast and may be taken in company with marinus, but 
I have not found it in the estuaries. 
In 1889 and 1890 this species occurred to me more commonly than 
did A. marinus. 
Probably there are alternating but gradual periods of abundance 
and scarcity in the occurrence of the two species; and I indeed 
noted that, in 1909, when marimus could be obtained in greater 
numbers than ever I saw it before, robina did not oecur to me at 
all. It is not easy to appreciate the cause of a definite struggle for 
existence between these two species, because, although occasionally 
met with together, the natural habitat of robinii seems to be much 
nearer the Laminarian zone than that of marinus. It was in the 
domain of the latter species that the submarine Hemipteron Aépo- 
philus was first discovered, and it has always been in that region 
that I have taken it in any quantity at Batten. In my experience 
it will be only by the lucky capture of stray individuals that Aépo- 
philus will be obtained where marinus abounds, i.e. in the upper 
reaches of the shore, below high-water mark. 
Notr.—Professor Miall, in his Natural History of Aquatic Insects, 
1895, p. 376, speaking of Aépus, says: “ The eyes are very curious. 
A chitinous plate protects and almost entirely covers them, leaving 
