1905.] CAPE VERDE MARINE FAUNA. 179 



these spaces ai'e the habitat of a rich fauna ; they are often 

 practically filled with Lamellibranchs and free-living Gastropoda, 

 while Polychpeta, SipuncuHds, small Crustacea (especially Amphi- 

 poda), Nemertines, and even Centipedes can be washed out in 

 great abundance. Boring Lamellibranchs (Liilioiiliagus sp. ?) are 

 common, sometimes astonishingly so, but Polychpeta and Sponges 

 of this habit are far rarer than in the pure Alga or Coral of the 

 shore-pools and bottom below tide-leveL Further north still, 

 where tlie sui'f breaks sti-ongly, the surface of the incrustation 

 becomes more or less bare of the mossy weeds and more or less 

 foliaceous, and on breaking into its smooth portions the propoi-tion 

 of Vermelus-tvAiQ^ is found to have greatly decreased. Fiu-ther on 

 are inaccessible rocks, covered with the light brown branched 

 nullipore described above. 



In some localities, e. g. the promontories just south of St. Yin- 

 cent Harbour, an Eupsammid coral forms the lower part of the 

 band of incrustation. This is always in a friable condition, and 

 large pieces can be detached by the bare hand. 



The incrustation is soft but tenacious, so that a crowbar must 

 be driven in several times before a piece can be detached. Indeed, 

 I found the best way of breaking it from the rocks to be b}'^ 

 hammering in the blade of a spade. I saw no evidence of pieces 

 being broken away by the waves, so that the causes of the limita- 

 tion of these growths to masses I'arely so much as one foot thick 

 ai^e not evident. Owing to the limitation of the zone to so narrow 

 a band of these steep shores, continued growth would result in 

 the formation of an unsupported shelf, which would at once be 

 broken away by the sea. But I believe the action of boring- 

 organisms to be more important. Physical conditions doubtless 

 are the prime factors in determining the balance of life, and here 

 they seem to have given the predominance to the agents of 

 destruction, while the cold currents from the north account for the 

 subordinate position of the Corals. A great amount of rock- 

 formation is going on at depths of from 5 to 20 fathoms. Where- 

 ever I have dredged in from 5 to 10 fathoms (St. Vincent, Porto 

 Praya, and Bonavista, text-figs. 26, 25, and 24), nodules of 

 TMSSv^ovtiLitliothcminion'^ are strewn abundantly over the bottom. 

 From 10 to 20 fathoms two more delicate kinds occur, one being 

 soft and foliaceous, the other consisting of thin and brittle 

 branches. The fate of these I do not know, but of the nodules 

 the great majority are rendered rotten by Sponges and boring 

 Polychpeta, finally breaking down to a grey mud. Among and 

 below these Algfe there is a coarse sand formed almost entirely 

 of a large foraminiferan. This covers practically the whole floor 

 of St. Vincent Harbour between the 5 and 20 fathom lines, but 

 finer sand and mud are plentiful in Porto Praya, and sand of 

 volcanic origin in Bonavista. In St. Vincent the resulting mud 

 from the destruction of the organic rocks appears to be carried to 



* Herdman's ' Peaii-Fisliing Report ' contains an excellent illustration of these 

 But in Ceylon the agents of destruction seem to be different. 



