C. F. ROUSSELET ON BRACHIONUS BAKERI. 329 



all its varieties, and absent in all other species of Brachionus, 

 are the following : — 



1. The ventro-posterior part of the lorica is prolonged, and 

 forms a tubalar sheath round the base of the foot as shown in 

 the side and ventral views, Figs. 2 and 3. This sheath stands out 

 nearly at right angle to the ventral plate, and its length is sub- 

 ject to variation, but it is always distinctly present in all the 

 varieties of this species. On the dorsal side of this sheath a 

 sub-square piece is cut out, the edges of which form the so- 

 called spines bounding the orifice of the foot described by Mr. 

 Gosse. This shelly tube or foot-sheath is mentioned by Ehren- 

 berg, but is omitted in Gosse's description. In all other 

 known species of Brachionus the foot opening is merely a 

 rounded hole in the ventral plate, with often a sub-square 

 piece cut out of the dorso-posterior plate, but there is no 

 approach to a tube. 



2. The median anterior spines, or antlers, curve outwards, and, 

 when long enough, are in addition bent downwards over the 

 head of the animal. This character again is mentioned by 

 Ehrenberg and omitted by Gosse. The anterior spines vary 

 very much in size ; they may be as long as represented in 

 Fig. 4, or as short as in Fig. 8, but they have always a distinct 

 tendency to curve outwards, whilst they are merely straight 

 in the other species of Brachionus. 



3. Another important character, and one which most ob- 

 servers would place first, are the two postero-lateral spines of 

 the lorica. As will be seen by the figures on Plate XVI., these 

 spines are subject to the greatest possible variations ; they 

 may be extremely long and narrow, or very short and stout, or 

 even absent altogether, divergent, parallel, or convergent. 

 These differences in shape, size, and direction of the posterior 

 spines have given rise to a number of specific names which 

 cannot be admitted ; even Ehrenberg's B. brevispinus is but a 

 variety of bakeri as he states himself. Gosse's figure of B. 

 bafceri on Plate XXVII., Fig. 8, of the monograph shows abnor- 

 mally broad posterior spines ; no doubt such a variety exists, 

 but I have not yet seen it, and it is certainly not the ordinary 

 type. The anterior median spines are drawn as forming a very 

 sharp angle between them, which I consider can hardly be 

 correct. The stout dorsal antenna projects between these spines, 



