lOI 



The above table appears to show that muriceid life is most abundant at a depth of 50 

 to 100 meters, and that there is abrupt falling off below the 100 meters line. 



An element too often neglected in such tables, and one that has lead to considerable 

 error in the discussions of bathymetric distribution in the past, is the actual number of hauls 

 of the dredge, or other appliance for securing bottom-living specimens, that was made in each 

 of the bathymetric zones under discussion. While it is impracticable to ascertain the exact number 

 of successful hauls made in each of the above zones during the investigations made by the 

 Siboga E.xpedition, a fair approximation of the relative numbers can be arrived at by noting 

 the entire list of stations, and the depth recorded for each. In this way we can to a great 

 extent eliminate the error mentioned above. We iind that there were about 100 stations where 

 the depth was from i to 50 meters, and that 44 species were collected at these stations. There 

 were about 36 stations between 50 and 100 meters, and 60 species collected. Between 100 

 and 200 meters there were but 15 stations, while the relatively large number of 27 species 

 was collected. There were about 50 stations between 200 and 500 meters, and here but 15 

 species were secured. A proportionally large number, about 1 30 stations, found a depth of 

 over 500 meters (many of which however did not secure specimens from the bottom) and but 

 1 2 species were secured. 



The difference in the vertical extent of the zones adopted in the table must also be 

 taken into consideration. If we combine the first and second and consider them as one zone 

 for purposes of comparison with the third, we find that they include 136 stations at which 109 

 species were secured. That is, there were just about 80 species to each 100 stations. Turning 

 our attention to the third zone (100 to 200 meters) we find but 15 stations, but these 15 stations 

 yielded 27 species the rate per 100 stations being 180. Thus we see that the third zone is 

 really the richest of all, yielding more than twice as many species per station as were found 

 in the combined i^' and 2"^^ zones. 



There seems to be a rather abrupt falling off below the depth of 200 fathoms, as but 

 15 species were collected from about 50 stations at depths of from 200 to 500, a zone of 

 three times the vertical extent of the third. The diminution is still more marked at depths 

 below 500 fathoms, where a relatively large number of stations were explored (about 130) and 

 but 1 2 species secured. 



The diminution is not so abrupt, however, as it appears from the table, on account of 

 the large number of stations at the greater depths at which no dredge or trawl was used. 

 Thus out of the 50 stations between 200 and 500 meters, 22 appear not to have been explored 

 with appliances for securing the animal life of the bottom. Taking this fact into consideration, 

 it appears that there were 28 stations effectively explored for animal life at the bottom at 

 depths between 200 and 500 fathoms, and that 1 5 species were secured, or about i to each 

 two stations. This still indicates a rather abrupt diminution of species below the 200 meters 

 line, and the evidence is the same for depths below 500 meters. 



It thus appears that the Muriceida; are much less abundant in the deep sea of the region 

 explored by the Siboga than in the shallower portions with a depth of less than 200 meters, 

 and that the maximum development in species is in the zone between loo and 200 meters. 



