. Bulletin of the British Museum (Natural History). E. TREWAVAS INTERRELATIONSHIPS OF THE SPECIES OF PELMATOCHROMIS It is to P. nigrofasciatus and not P. ocellifer that Thys is referring when he writes (1968a) that P. congicus is a specialized form derived from P. ocellifer. With the substitution of the name I would agree with this opinion, but the speciaUzation has gone so far that P. congicus is best considered as a separate genus. P. ocellifer and P. huettikoferi are alike in the dentition of jaws and pharynx in which they contrast with P. nigrofasciatus, especially developmentally. On the
. Bulletin of the British Museum (Natural History). E. TREWAVAS INTERRELATIONSHIPS OF THE SPECIES OF PELMATOCHROMIS It is to P. nigrofasciatus and not P. ocellifer that Thys is referring when he writes (1968a) that P. congicus is a specialized form derived from P. ocellifer. With the substitution of the name I would agree with this opinion, but the speciaUzation has gone so far that P. congicus is best considered as a separate genus. P. ocellifer and P. huettikoferi are alike in the dentition of jaws and pharynx in which they contrast with P. nigrofasciatus, especially developmentally. On the other hand P. huettikoferi differs from both Congo species in the colour-pattern, having no tilapia-mark, but instead a dark spot on the back below the site of the tilapia-mark of others, and its pelvic, dorsal and anal fins are less produced. P. ocellifer has a shorter series of epibranchial gill-rakers on the first arch than either of the other two species. Some other aspects of their structure will be considered in discussing their alleged relationship with Tilapia. I propose a new genus, Pterochromis, for the type species P. congicus Boulenger, distinguished from Pelmatochromis by its large oblique mouth, long slender gill- rakers and more specialized dentition. The two genera have in common the following features :- Apophysis for the upper pharyngeals formed by the parasphenoid alone; all teeth unicuspid in adult; pad on roof of pharynx sessile; microbranchiospines present; lateral lines overlapping by only one or two scales if at all, the upper separated from the dorsum posteriorly by li scales; scales cycloid, partly roman, partly gothic (see fig. 10).; vertebrae 26 or 27, mode 26; scales 27 or 28 in lateral hue series. They are distinguished from each other as follows :- ^jjBgfcjr^f^i.^ V y/i '7*'?'./ '7/--^.'- ;. -' â â¢<. .7 â. ,X m fm ''Mm'. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabili
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