238 bulletin: museum of comparative zoology. 



D and E) as summer forms of O. tripos baltkum, the one (fig. D) as 

 forma lata and the other as forma lineata. He subsequently introduces 

 the second or gamete hypothesis, which will be discussed later, but favors 

 the first interpretation, however, for he revises the nomenclature of these 

 species of Ceratium, and throughout his paper refers to Ceratium " linea- 

 tum " (anterior schizont in fig. E) as C. tripos balticum forma lineatum 

 and to C. minus Gourret (anterior schizont in fig. D) as G. tripos baltica 

 forma lata f. nov. From the discussion and treatment of these forms in 

 his tables he evidently regards all G. lineatum and C. minus which were 

 found in his plankton collections from the Baltic as well as those found 

 in heteromorphic chains as summer forms of C. tripos var. balticum, and 

 gives figures of a number of isolated individuals of typical 0. lineatum 

 Ehrbg., which he also designates as such forms of C. tripos. 



It is difficult, with merely the outline figures of Lohmann to examine, 

 to pass critical judgment upon the specific identity of the forms he 

 figures. Certain differences, however, between the anterior heteromor- 

 phic schizont of his chain (III b) (fig. E) and the typical C. lineatum 

 shown in his figures III c, d, f, and g of detached schizonts lead me to 

 doubt the specific identity and genetic continuity of the two forms. (His 

 figure IV g is reversed ;,that is, it represents the dorsal side seen from the 

 ventral face.) Ceratium lineatum has a midbody of different proportions 

 from the heteroinorph. The following table of proportionate measure- 

 ments, using the transdiameter of the individual as the unit of 

 measurement, expresses these differences : 



Ceratium lineatum, Lohmann's 

 figures III c, d, f, g, extremes 

 and averages. 

 Heteromorph. Extremes. Averages. 



Length of midbody 1.4 (1.6-1.9) 1.75 



Distance from girdle to 



Postmargin in axial region 5 (.60-.65) .63 



Length of left antapical 82 (.75-1.2) 1.0 



Length of right antapical 43 (.43-70) .62 



Transdiameter of figure in millimeters . 11. (7.5-9.) 8.1 



Ratio of two horns 1:1.9 1:1.6 



The midbody of C. lineatum is absolutely smaller, relatively narrower 

 and longer, and tapers more gradually into the apical horn. Its two 

 antapical horns are not so unequal in length. Lohmann states that 

 the volume of the smallest individuals of f. lineatum is only one tenth of 

 that of C. tripos balticum. The possibility of a confusion here by Loh- 

 mann of C. lineatum and Ehrenberg's minute species C. eugrammum, of 



