~ extremity of radial joint. 
268 Transactions. —Z oology. 
The discovery of Desis robsoni, and its highly aquatic and marine habits, 
clear up Dr. Koch’s doubts as to the voluntarily aquatic habitat of Desis 
martensit, 
In reply to some enquiries of mine, Mr. Robson gives the following 
additional information as to the mode of life of this interesting spider :— 
** The nests of this spider do not, in my opinion, occur below low water; 
but it is difficult to state positively. The mouth of the Lithodomus hole in 
which the nest is made is often, if not always, under low water in a tidal 
pool, and the nest is only to be got at by breaking up the rock with a heavy 
hammer. The spider, when going to the bottom of a pool, on being dis- 
turbed, does not take down an air-bubble so far as I could see, and is able 
tolive a considerable time without air or only the small amount to be found 
in sea-water. I have kept them alive for several days in a bottle quite full. 
The cocoons of eggs are found at the end of the hole and always quite dry. 
Ihave not seen these spiders at any place but Cape Campbell, and there 
not far above low-water mark, there being many feet of water over the 
rocks in which they live at high tide." 
Further observations on the habits of this spider are desirable. An 
examination of their nests might disclose the nature of their food. Also, if 
Mr. Robson is correct in stating that the mouths of the holes in which they 
live are always below low water, how are they supplied with air? A careful 
comparison of Desis robsoni with Koch's description and figures of Desis 
martensii, shows that these two spiders differ very slightly. The posterior 
pair of legs are much shorter relatively in Desis robsoni. The posterior row 
of eyes in Desis martensti are concave anteriorly, in D. robsoni very slightly 
concave posteriorly. The process on the radial joint of the male palpus 
differs in form in the two species, and there are only six teeth to the upper 
border of the fang groove in Desis robsoni, there being seven in Desis 
martensii. Walckenaer’s diagnosis of the genus founded on a single species 
needs revision now that three more species have been discovered. The 
arrangement and relative proportionate size of the eyes and the length of 
the legs vary from the characters as laid down by him in the Histoire des 
Aptéres. 
DESCRIPTION OF PLATE XII. 
Desis robsoni. 
1. Male, showing form and relative proportions of cephalothorax and falces. 
2. Lateral view to show elevation of cephalathorax, female. 
8. Anterior view of caput showing arrangement of eyes. 
4. Sternum, lip, maxillz, and falx, female. 
5. Epigyue, female. 
6. Radial and digital joints of palpus, male, as from beneath, b from outer side, ¢ 
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