Introduction. 



This paper, dealing with the Penasids and Steno- 

 pids, forms the first part of the memoir upon the decapod 

 Crustaceans taken during the "Michael Sars" North At- 

 lantic Deep-Sea Expedition in 1910. Subsequent papers 

 will treat of the other prawns and of the Reptantia in a 

 similar manner, and will contain a general account af the 

 decapod fauna of the Atlantic from the geographical and 

 biological points of view, based upon the material col- 

 lected by the Expedition. 



The technical terms used are those generally employed 

 in modern works. In stating the size of a specimen I 

 ahve made a departure from the usage hitherto common, 

 giving the lateral length of the carapace (measured from 

 the ocular sinus to the hinder edge of the carapace) where 

 not otherwise stated. I have introduced this innovation 

 because the total length is often very difficult to determine 

 accurately and, when the rostrum is included, this measure- 

 ment may give a false idea regarding the dimensions of 

 the animal, as the relative length of the rostrum differs 

 exceedingly, not only in the different species of decapoda, 

 but also in different individuals of the same species. 



For most species tables are inserted indicating (1) the 

 dimensions, i. e. length of carapace, (2) the bathymetrical 

 distribution, and (3) the number of specimens taken. The 

 depths are estimated as equal to half the length of wire 

 paid out (m. w.), and in the opinion of mr. Thor Iversen, 

 the captain of the "Michael Sars" during the Expedition, 

 this estimate is generally not far from the truth. 1 ) But 

 even if one knew the actual depth at which the appli- 



ances were towed, it must be borne in mind that an ani- 

 mal may occasionally be caught while hauling in. The 

 influence of this source of error is however considerably 

 lessened in the case of species taken in great numbers, 

 as the number of specimens caught during the short time 

 required to haul will always be small compared with 

 the number taken during the long time devoted to tow- 

 ing horizontally. The following abbreviations are made 

 use of: — 



mxp." 

 trl 3 

 1 sn. 



y- 



3 In. 

 m. w. 



= third maxilhped ) 



*,L 11 \ after Hansen 1896. 

 = „ pereiopod (trunkleg)J 



= silknet, 1 metre in diameter. 



= young-fish trawl (with an opening of four 



square metres). 



= large net, 3 metres diameter. 



= metres of wire paid out. 



In the tables indicating the catches, each specimen 

 is represented by a figure denoting its size, following 

 the sign for sex., e. g. <? 5 = a male with carapace 5 

 millimetres long; ? 67 cT 5-7 = two females and two 

 males, the length of carapace being respectively 6 and 7, 

 and 5 and 7 mm. The sign is used to indicate im- 

 mature specimens, the sex of which could not be deter- 

 mined. 



I take the opportunity of offering my thanks to dr. 

 Hjort for placing in my hands for examination the rich 

 collections from the Expedition he so succesfully carried 

 through. 



The printing of this paper, which was ready in manuscript in 1915, has been delayed by the fire in jan. 

 1916 and by war-time difficulties. Litterature appeared since 1915 has consequently not been considered. 



Bergen, jan. 1920. 



1 ) Subsequent scrutiny of the records has, however, shown that the depth attained may go up to two thirds of the length of wire 

 paid out. The steepness of the wire is apparently greater when a great length is out, on account of the lesser speed caused by the greater 

 resistance from the great number of nets which were attached to the single wire. See also J. Grieg: Brachiopoda etc. (in the present 

 volume), p. 5. 



