Bt Herdman on the " Olfactory TulercUr 259 



and pointing directly posteriorly. The fourth simple variation 

 is, like the two last, transversely elongated and symmetrical, 

 but is of a triangular form (Fig. 5). The base or posterior 

 end is very long, and is slightly concave posteriorly in its 

 centre ; the sides slope anteriorly towards the narrow opening 

 where the horns are bent abruptly inwards, and then coiled 

 outwards and upwards, so as to form a complete circle. 



Fig. 4. Fig. 5. Fig. 6. 



We now come to the commoner forms in which the tubercle 

 is not symmetrical, and in these it is easy to notice that the 

 prevailing type is an irregular lozenge, of which the left 

 hand angle is directed posteriorly, and the right hand one 

 anteriorly (Fig. 6). The posterior end of the organ forms an 

 angle which occupies the angle of the peri-tubercular area. 

 Both horns are bent inwards, but the left one usually passes 

 internally to the other, and is more coiled, the right hand one 

 being sometimes straight, and almost invariably overlapping 

 the left horn, so as to render the opening oblique or pointing 

 anteriorly and to the left. 



In one unsymmetrical variety noticed, and which occurred 

 only once, the opening was directed anteriorly, and to the 

 right. This was caused by the feeble development of the 

 right horn, which, in place of overlapping the left one, was 

 bent inwards, and approached it so as to reduce the size of 

 the opening and change its direction. 



It is comparatively easy in this species to fix upon a 

 characteristic form of tubercle; it is undoubtedly the lozenge- 

 shaped unsymmetrical variety with the right horn over- 

 lapping the left one, and directing the opening obliquely 

 anteriorly and to the left. 



The following description may be considered typical for 

 the species : 



Olfactory tiCbcrclc moderately large ; irregularly lozenge- 



