628 Mr. G. L. Bates on the 



(2) Gap ill the Spinal Tract in certain Sylviidre. 



In certain genera forming a very natural group, largely 

 African, of vvliieh Cisticula may be taken as typical, tliere is 

 a marked gap in the sj)iual tract immediately behind the 

 paddle, and the lower end of the saddle itself is often 

 emargiuate or cordate in outline. This gap is sometimes 

 entirely withont feathers of any kind, but usually bears a 

 few small semiplumes in a more or less regnlar row, but no 

 eontonr-feathers. It extends from the saddle halfway to 

 the oil-gland. The specimen of Calnuwcichia rufescens 

 figured had a few semiplumes on this part. Specimens of 

 Camaroptera griseoviridis had not even the semiplumes, 

 but had a peifectly bare gap from the saddle for 5 mm. in 

 the direction of the tail. The same was true in the one 

 specimen examined of Bathmedoma rufa and in one of 

 Macrosphenus concolor. In a half-Hedged specimen of 

 Prinia mystacea there was a perfectly bare gap extending 

 for 10 ram. — a long way in so small a bird ; but in adults 

 of the same species the corresponding portion bore a few 

 small semiplumes. 



Besides the species already mentioned, the following were 

 examined — generally more than one specimen of each — and 

 found to have this gap: — Cisficola erythrops, Buryiesia 

 bairdi, B. leucopof/on, Apalis binotata, Macrosphenus flavicans , 

 Camaroptera superciliaris, Sylviella virens, S. denti, and 

 Eremomelu badiceps. 



Some other species of small birds somewhat similar to 

 the above, and generally placed near to them, were found to 

 be ivithout such a gap in the spinal feather-tract. Among 

 these may be mentioned PhyVoscopiis troch'ilus, Stiphrornis 

 .rant hoy aster, and Hylia prasina ; in these the spinal tract, 

 though narrow behind the saddle, was continuous, bearing 

 contour-feathers all the way. 



The gap here de^cribed is doubtless a degeneration of the 

 portion of the spinal tract most clearly overlapped by the 

 long and abundant plumage of the saddle. But in birds of 

 other groups examined in which the feathers of the saddle 



