13 



covered with rough tubercles. In front of the cervical groove 

 the spines, according to Senna, are arranged as follows 



Rostrum + 1, 1, 1, 1, 2, 2, 



in the male, and in the female either the same or, 



Rostrum + 1, 1, 1, 2, 2. 



In the specimens taken by the Helga these spines are not 

 always well developed. It is especially difficult sometimes 

 to say whether a spine is double or not. The one which lies 

 just in front of the cervical groove is very often single, or has 

 one half much larger than the other, or is altogether rudimentary. 

 Behind the groove there are three double spines, but often some 

 of these are very slightly developed. The arrangement of the 

 carinal spines on some of the Irish specimens is as follows. 

 (The semicolon marks the position of the cervical groove, and 

 r signifies that the spine is rudimentary.) 



Rostrum +1, 1, 1, 2, Ij ; 2, r, 2. 



Rostrum + 1, 1, 1, 2, r ; r, r, 2. 



Rostrum + I, 1, 1, 1, 2, Ij ; r, r, 2. 



Rostrum 4-1, 1, 1, 2, Ij ; 2, 2, 2. 



Rostrum + 1, 1, 1, 2, r ; r, r, 2. 



The cervical groove is situated almost exactly half-way be- 

 tween the rostrum and the hind margin of the carapace. It is 

 well marked, and at a point rather nearer the median line than 

 the margin it divides into two. The posterior branch cuts 

 the margin almost at right angles, whereas the anterior, which 

 is the fainter of the two, slants forwards, and meets the margin 

 at an acute angle. From the hind branch of the cervical groove 

 a low ridge furnished with about twelve to fourteen small 

 teeth runs backwards parallel with the margin to the posterior 

 end of the carapace. It is almost twice as far from the median 

 carina as from the lateral margin. From the middle of the 

 anterior branch of- the cervical groove to the orbital sinus 

 there is a curved row of four or five spines, which are not situated 

 on a ridge. On the cervical groove itself, besides the two 

 central spines forming part of the median carina, there is a 

 single smaller spine on each side above the bifurcation, and 

 three or four very small ones on the hind branch below it. 

 Besides the larger spines, the position of which has been indicated, 

 there are numerous very small ones scattered over the surface 

 of the carapace ; they are particularly plentiful about the 

 borders of the cardiac region, and all of them aie directed for- 

 wards. 



On the lower surface of the carapace there are at each side 

 two oblique carinae armed with small teeth. The external or 

 upper of these submarginal ridges begins just opposite the base 

 of the antenna and runs backwards towards the postero-lateral 

 angle of the carapace. Its anterior end is marked by a large 

 spine. The teeth are fairly large in the front portion, but they 



