SCHIZOPOHELLA LINEARIS. 2¥d 



Range of Variation. Apart from the usual superficial 

 differences dependent upon the degree in which the cal- 

 careous crust is developed, the chief variation in this well- 

 marked species takes place in the position, size, and 

 direction of the avicularia. Normally there are two, which 

 usually occupy corresponding positions on each side of the 

 cell, though in some cases there is a great deal of irregu- 

 larity. Frequently, however, these are replaced, on one 

 and the same colony, by a single central avicularium, 

 which is often very prominent and of large size. In some 

 cases the avicularium is borne on the side of a short 

 rostrum, placed a little below the oral sinus. Occasion- 

 ally a large raised avicularium is met with near the 

 bottom of the cell, placed transversely ; and the ooecium 

 is sometimes attended by one or two, in addition to the 

 oral pair. 



In an Algerian specimen the latter are placed almost 

 close together, facing one another, below the inferior 

 margin of the mouth, and are larger and much more 

 elevated in front (almost vertical) than in the usual form. 

 In another very marked variety {mamiUata), which is 

 also from Algiers, the avicularium is single, placed 

 immediately below the oral sinus, and borne on a 

 mamillary enlargement of the front wall of the cell, the 

 mandible pointing straight outwards. The position is 

 constant and invariable; the cells are granular, tumid, 

 and irregularly disposed; and there is (in the specimen 

 which I have examined) a total absence of the rudimen- 

 tary ovicelligerous cells that are so characteristic of 

 S. linearis. This has somewhat the appearance of a 

 distinct species ; but, on the whole, and especially consi- 

 dering the great variability in the position of the avicu- 

 larium, which distinguishes the present form, I believe 

 that it is more properly ranked as a variety. 



