BY E. P. KALLMANN. 



403 



(though occasionally exceeding) 45'. The basal extremity is 

 evenly rounded off, not tylote; the portion of the shaft between 

 it and the point of flexure is usually straight or very nearly so; 

 the remainder of the shaft is, almost without exception, perfectly 

 straight, and tapers gradually to a sharp point. Basally, for at 



Text-fig. 2. 



Rhahdosigma mammiUata — a, fullj'^-grown rhabdostyli; h, immature rhab- 

 dostyli ; c, abnormal forms of rhabdostyli ; d, larger sigmata ; e. 

 smaller sigmata. 



least one-fourth of the entire length of the spicule, and also 

 apically, for about the same distance, the shaft is invariably 

 quite smooth; but not infrequently, over some portion of its 

 intermediate region, there occur a few small, perpendicularly 

 directed spines, the largest not exceeding Ifx in height. In the 

 case of an unusually large number (at least 25%) of the (other- 

 wise fully-grown) spicules, the axial canal remains unclosed 

 apically, and is then frequently very conspicuous, occasionally 

 attaining a diameter of as much as 4-5/x. Also of rather frequent 

 occurrence are abnormal forms (Text-fig. 2, c), generally with the 



