27 



of the Pacific from Alaska to San Diego I have found this species 

 in a large number of collections and am convinced of its distinct- 

 ness from both C. lineatum and C. furca^ with neither of which it inter- 

 grades, and that it is, in all probability, the form the Ehrenberg re- 

 cognized and must therefore be designated as C. eugrammum (Ehrbg.). 

 The accompanying figures give, for comparison, dorsal views of 

 four species , three of which have been subject to great confusion in the 



S faunistic literature of the group and the fourth (C teres) has been re- 

 rently described by me. 



C. eugrammum is the smallest species in the genus. It has a rela- 

 tively narrow midboy with steep lateral margins of the epitheca. Its 



' antapicals are straight, and usually not diverging, and the hypotheca 

 is but Uttle contracted between the girdle and the bases of the antapicals. 

 It differs from C. furca in its smaller size, greater delimitation of apical 



horn from midbody, shorter antapicals, marked Unear striae and more 

 dehcate habit. From C. teres it differs in the more robust habit and 

 presence of striae, in the straight, rather than convex, sides of epitheca 

 and hypotheca and in the absence of distal contraction of the latter. It 

 thus lacks entirely the broadly fusiform outline which C. teres presents. 

 From C. lineatum it differs in its narrower midbody and steeper slopes 

 of the antero-lateral margins of the epitheca. It is evident that C. line- 

 atum and C. eugrammum are closely related as shown by their form 

 and surface markings. They differ however in one important structural 

 character, viz: — the precingular plate (fig. 2 IV) which is present in C. 

 lineatum but apparently not in C. eugrammum. The normal number 

 of precingular plates in the genus Ceratium is three but in C. lineatum 

 and C. furca in some individuals , at least, an additional suture line 

 passes from the suture between the apical and precingular series to the 

 girdle plate, splitifig the right precingular into two parts. This accessory 



