686 MR. G. TATE REGAN ON THE 



Nyassa resembles Yictoria and differs notably from Tanganyika. 

 In the Nyassa species the caudal fin is truncate or emarginate, 

 and appears to be always nearly completely covered with small 

 scales in the adult fish ; this feature, the prevalence of a few 

 distinctive types of coloration, and the absence of evident 

 i"elationship to species found elsewhere lead to the conclusion 

 that the Nyassa species are a natural group and may perhaps 

 have evolved in the lake from a single ancestral form. This 

 conclusion is fortified by the study of such skeletons as are 

 available. 



The differences in the pharyngeal dentition between closely 

 related species are sometimes very striking ; the best examples 

 of this are R. tetrastigma and H. placodon, and H. similis and 

 H. kirhli ; these cases make it evident that it is not desirable to 

 regard the development of large, round, blunt pharyngeal teeth 

 as warranting generic separation. 



Synopsis of the Nyassa Species. 



I. Snout not longer than postorbital part of head. 



A. Pectoral fin with series of spots on the rays. 



Lower jaw projecting 1. limngstonii. 



Jaws equal; depth of body 2f to 3 in length 2. poly stigma. 



Jaws equal; depth 2f in length 3. maculimanus. 



B. Pectoral fin immaculate. 



1. Prffimaxillary pedicels not extending beyond anterior edge of orbits. 



a. Body with a series of dark spots on back alternating with a series on or 



abiive middle of side, or uniting with them to form irregular cross- 

 bars. Jaws equal; outer teeth mostly bicuspid. 



Pharj'ngeal teeth small ; spots very large 4. simulans. 



Middle pharj'ngeal teeth enlarged, blunt ; caudal peduncle 



1 J to If as long as deep * 5. suhocularis. 



Middle pharyngeal teeth enlarged, blunt ; caudal peduncle 



a little longer than deep 6. ornatus. 



b. Body with 6 dark cross-bars. Lower jaw projecting; outer teeth 



bicuspid. 



Pharyngeal teeth small 7. JoJmstoni. 



Lower pharyngeal with a group of enlarged blunt teeth ... 8. se.vfasciattis. 



c. Body with a dark lateral stripe, slightlj^ curved anteriorly, from head to 



caudal tin. Outer teeth bicuspid. 

 a. Lower jaw a little projecting; middle pharyngeal teeth stout and 



blunt 9. kirkii. 



(3. Jaws equal; pharyngeal teeth small. 



Caudal truncate or slightly emarginate 10. similis. 



Caudal rather deeplj' emarginate; 45 to 60 teeth in outer 



series 11. breviceps. 



Caudal rather deeply emarginate ; 24 to 30 teeth in outer 



series 12. microstoma. 



d. Body with a dark lateral band on tail, continued forward as a series ot 



spots. Teeth conical. Lower jaw projecting. 13. urotceiiia. 



e. Body with a straight dark band or stripe from head to caudal fin. 



Teeth conical. Lower jaw projecting. 



a. Mouth little oblique, below level of eye. 



Caudal truncate or very slightly emarginate 14. fuscotceniafus. 



Caudal distinctlj' emarginate 15. holotcsnia. 



B. Mouth very oblique, anteriorly on a level with ej-e. 



Depth of body 2| to 24 in length 16. strigatns. 



Depth of body 4 in length 17. dimidiatus. 



