105 



are six of these spines located as follows. A minor one {a) at the posterior 

 end of the fin at the left of the longitudinal furrow plate near the median 

 line; another (b) at the junction of plates 12, 13, 14 and Ì.5; one [c) at 

 the junction of ü, 12 and 15, on the left antapex, near which on the 

 suture line between ü and 12 is an accessory spine [d). Another minor 

 spine (e) is found on the oppisite side to this pair, at the junction of 9, 

 10 and 15. The major spine (/"), on the right antapex, is located near 

 the junction of 9, the longitudinal furrow plate. [16], and the antapical 

 {15} upon which it is apparently located. The spines are often very 

 short and minute. 



On the suture line between plates 14 and 16 arises a broad deli- 

 cately reticulate fin which overhangs the longitudinal furrow and covers 

 nearly one half of it. It is not usually develoiied to the degree shown 

 in the figure in most individuals. 



The contents of the theca are very dense, due to the closely packed 

 chromatophores. The presence of many empty thecae in my material is 

 indicative of the escape of the contents , a very common jDhenomenon in 

 this genus when sporulation occurs. In one instance an empty theca 

 was noted which showed the evidences of recent division along suture 

 lines running from the right shoulder to the left antapex. 



The entire absence of any midventral area and pit and of a left 

 intercalary plate of the epitheca of this organism precludes its inclusion 

 in the genus Heterodiniimi. It is unquestionably a Gonyaidax with 

 thecal plates typical of that genus. Its occurrence in Alaskan waters, and 

 the provious records of its apparance in the Plankton off the coasts of 

 Norway , Iceland , Shetland Islands , and Finland , indicate that it is a 

 boreal neritic species of wide distribution. I find no characters in 

 Alaskan forms which would justify even a varietal distinction from the 

 Atlantic form. 



The removal of the species triacantha fi'om the genus Heterodinium 

 leaves the distribution of the known species of that genus exclusively 

 in tropical and warm temperate waters as will be seen in my (: 06) table 

 of their distribution. 



Berkeley, California, Jan. 10, 190G. 



