no. 1404. PA RA STTIC COPEPODS— CA LIGIDM— WILSON. 655 



Total length 3.5 mm. Length of carapace 2.5 mm.; width of same 

 2.3 mm.; length of genital segment 0.9 mm.; length of abdomen 

 0.25 mm. 



The collection of the National Museum contains one lot of this 

 interesting species sent from England by Rev. A. M. Norman. It is 

 numbered 8105, and was obtained from the gill cavity of Pagellus 

 Ct ntrodontuB. The species was originally discovered by Baird and 

 described by him in 1850, and no further description has ever been 

 given. Indeed, so far as known, it was not even noted by any other 

 author until Bassett-Smith in 1899, and he simply gives the name. 



The description here given supplements that of Baird in many par- 

 ticulars, especially with regard to the appendages. 



Attention should be called to the lateral plates or spines on the sides 

 of the free segment which are not mentioned by Baird, but which are 

 important as a connecting link between this form and those in the 

 following subfamily, the Euryphorinae. The latter are characterized 

 by the presence of just such plates in all the species, while the Caliginse, 

 which are here discussed, have no such plates or processes. 



In the present species the plates are so small as to be easily over- 

 looked, but if the large aprons at the bases of the second legs be re- 

 moved and the copepod be then examined the plates appear plainly. 

 Most of the Euryphorinse are unable to swim about freely, and with 

 this lack of free locomotion there appear the dorsal plates on the thorax, 

 or abdomen, or both. 



It is interesting to find that the beginnings of these plates are found 

 among forms which still retain the ability, if not the disposition, to 

 move about freely. 



Another detail of anatomy is equally interesting, and this also was 

 overlooked by Baird. The upper surface of the genital segment pro- 

 jects considerably over the base and sides of the abdomen, so that the 

 latter is partially concealed in dorsal view. But the posterior margin 

 of the genital segment is cut in a deep semicircle, which reveals most 

 of the dorsal surface of the abdomen. We have here, therefore, the 

 initial step in the disappearance of the abdomen; the genital segment 

 is deeply incised to receive it, and it is attached on the ventral surface 

 so as to be partly concealed. The second step is found in Lepeoph- 

 tln ii'i/s dis8vm,ulatu8^ where the abdomen is attached as far forward on 

 the ventral surface, but the genital segment is no longer incised, and 

 consequently almost entirely covers the abdomen. The third and 

 last step is the complete disappearance of the abdomen in the genus 

 . \nur< t< s. 



