NATURAL SCIENCES OF PHILADELPHIA. 139 



This is a very distinct species, readily distinguished by the small mouth 

 and short intermaxillary processes, as well as by its dimensions and the color. 



A single specimen is in the collection of the Smithsonian Institution, to 

 which it has been transferred from the former National Institute of the City 

 of Washington. There is no indication of locality, but it is probable that it 

 was sent from Liberia. With it are three other species, a foetal Rhirtobatus, 

 a new Clarias* and a new Mormyroid,\ all in a poor state of preservation. 



Three African genera of Chromoids appear to be now known, all of which 

 differ from the American ones. All have a regular form, interrupted lateral 

 line, large scales and three anal spines. They may be briefly distinguished as 

 follows : 



Tilapia A. Smith, A. Dumeril. 

 Chromis Heche! , Miiller, Peters, Giinther, (nee Cuv.) 

 ? Coptodon Gervais. (? = Haligenes Gthr.) 



Corpus ovatum ; caput breve ; dentes apicibus oblique espansis, uni vel bi- 

 emarginatis, in maxilla superiori triseriales, inferiori biseriales. 

 Type. Tilapia nilotica. 



Haligenes G-Linther. 



Corpus ovatum; caput breve; dentes apicibus oblique expansis, uni vel 

 biemarginatis ; in maxilla superiori biseriales, serie interna minores, infe- 

 riori uniseriales. 



Type. Haligenes Tristrami Giinther. 



Hemichromis Peters. 



Corpus oblongum ; caput oblongo-conicum, acutum ; dentes conici, apici- 

 bus nigri, in maxilla superiori biseriales, serie interna minuti, inferiori uni- 

 seriales. 



Type. Hemichromis fasciatus Peters. 



* Clarias la-viceps Gill. Height at anus a lenth of length; head (laterally) a sixth; its 

 breadth an eighth ; the surface smooth ; maxillarv barbels lwice as long as head. 

 D. 86. A 61. 



t Marcusenius brachyistius Gill. The height in front of the anal fin equals a fit' li of 

 the length, exclusive of the caudal, and scarcely exceeds the length of the head. The 

 distance of the short dorsal from the snout is three and a half times ('69) greater than 

 the head's length; the anal has about ten rays before and four behind lhe dorsal. The 

 pectorals are shorter than the head ( 15) and scarcely extend as far as the bases of the 

 ventrals. The head is decurved and the snout convex. All the teeth (about six in each 

 jaw) are em irgin.ued. 



D. II. 1. 14. A. II. 1. 24. Scales 50; between ventrals and lateral line 10 rows; in 

 9 

 front of anal I. 



9 

 Widely distinguished from its congeners (itf. anguilloides, M. Tucheyi and M. zamba- 

 nerije) by the radial and scale formula?. 

 The Mormyroids are divisible as follows: 



I. Dorsal very long. Vomer covered by anterior processes of pala- 



tine bones; cerebellum entirely concealed above. . . Mormyrin.e. 



Muzzle tubulifurin (M. caschive Has.) ...... Mormyrus. 



Muzzle obtuse (M. Hasse/quistii Geoff.) Mormyrodes. 



II. Dorsal more or less abbreviated. Vomer uncovered. Cerebellum 



and quadrigeminal bodies more or less exposed above. . . Petrocephalin^e. 



A. Snout not produced ; mouth not continued to vertical of eyes. 



a. Anal (25 50), not more than twice as long as dorsal 



Lower jaw prominent, M. anguilloidex. L . . . Motmyrops. 

 Upper jaw longer, (M. cyprinoidex L.) .... Marcusenius. 



b. Anal three times as long as dorsal. 



Palatal teeth pixiform (M. dorxalix Geoff.) . . . Hyperopisus. 



B. Snout produced. Mouth under eye, (M banc Val.) . . Pe.rocephalus, 



1862.] 



