1911] K of Old: The Genus Gomjaulax. 193 



may be smooth or reticulate, and the mesh may be predominantly 

 linear, vermieulate, polygonal or irregular. None of these fea- 

 tures affords any satisfactory criterion for a genuine diagnosis. 



(2) The displacement of the girdle in a descending spiral 

 with the distal end one or more girdle widths posterior to the 

 proximal occurs in all species of the genus. It is this character 

 primarily which distinguishes Gonijaulax from Amphidoma in 

 which the displacement is at the most but slight. 



(3) The longitudinal furrow should not be considered as 

 extending, as Stein (1883) supposed, anteriorly upon the 

 epitheca to the apex. There is no basis in the skeletal mor- 

 phology for this interpretation, and there is no suggestion of 

 such an extension of the furrow in the external appearance in a 

 number of species which belong in this genus. The midventral 

 apical plate {!' fig. A) in Gonyaulax which is homologous with 

 the diamond-shaped " Rautenplatte " of Peridinium, extends 

 from the apex posteriorly until it meets an anterior extension 

 of the ventral area (v. a., figs. A and B) and thus separates the 

 precingular series in the midventral line between preeingulars 

 1" and 6". In most but not all species of Gonyaulax this ventral 

 apical 1' is a narrow plate. When suture lines are marked by 

 thickenings of the wall, as for example in G. ceratocoroides [see 

 Murray and Whitting (1899, pi. 30, fig. 6)] this plate, in conse- 

 quence of these thickenings, lies at the bottom of a depression 

 between elevated ridges. This, however, does not occur in all 

 species and the trough thus formed is not a part of the furrow in 

 which the longitudinal tlagellum lies any more than are similar 

 depressions between ridges elsewhere on the thecal wall. (See 

 Murray and Whitting 's figures). 



(4) There is no trace of evidence whatever that this so-called 

 anterior extension of the longitudinal furrow to the apex ever 

 functions as a longitudinal furrow; that is, that it serves as a 

 trough for the longitudinal flagellum, whose normal position is 

 in the furrow running posteriorly from the flagellar pore. 



To regard this plate as a part of the longitudinal furrow is 

 thus to assign to it a function which it does not have, and to 

 obscure its morphological relations. Furthermore, to make this 



