INTEODTJCTION. 



XXXI 



10. 

 11. 

 12. 

 13. 

 14. 

 15. 

 16. 

 17. 

 18. 



Pacific. 



Philypnus maculatus. 

 Eleotris picta. 

 Dormitator lat'tfrons. 

 Gobioides peruamts. 

 Gerres simillimus. 

 Gerres californiensis. 

 Gerres peruvianus. 

 Gerres lineatus. 

 Centropomus medius. 

 Centropomus viridis. 

 Centropomus robalito. 

 Centropomus imionensis. 

 Pomadasis bayanus. 

 Mugil thoburni. 

 JElurichthys scutatus. 

 JSlurichthys pinnhnacnhttus 

 Galeichthys guatemalciisis. 

 Arius lirojjus. 



Atlantic. 

 P. dormitator. 

 E. pisonis. 

 D. macidatus. 

 G. broussonetii. 

 G. cinereus. 

 G. harengulus. 

 G. olithostomus. 

 G. plmnieri. 

 C. pjectinatus. 

 C. undecimalis. 

 C. ensiferus. 

 C. alt us. 

 P. crocro. 

 M. incilis. 

 ^-E. isthmensis. 

 JE. bagre. 

 G. assimilis. 

 A. melanopus. 



In several cases there is identity in the number of fin-rays, scales (when present), 

 and gill-rakers between the members of a pair of species. This applies to the 

 following : — Lormitator maculatus and D. latifrons, Gerres lineatus and G. jdumieri, 

 Centropomus rolalito and C. ensiferus, Centropomus unionensis and C. altus, Mugil 

 thoburni and M. incilis, JElurichthys scutatus and ^. isthmensis, Galeichthijs guate- 

 vialensis and G. assimilis, Arius melanopus and A. liropits. 



In other cases there is agreement in the number of fin-rays and of gill-rakers, but 

 not of the scales (e. g., Gerres simillimus and G. cinereus, Gerres jjeruvianus and 

 G. olithostomus, Centropjomits medius and C. pectinatus, Pomadasis bayanus and 

 P. crocro). In the last pair the slight difference in the size of the scales is uniform ; 

 a longitudinal or transverse count on any part of the body will probably give a larger 

 number for the Pacific form. In Centropomus medius and C. pectinatus the scales 

 differ in number only above the lateral line, especially anteriorly, where they are 

 always smaller in the Atlantic species. Gerres peruviamis is identical in scaling with 

 G. olithostomus, except in the thoracic region, where it has distinctly fewer and larger 

 scales, whilst the only tangible difference in the scaling of Gerres simillimus and 

 G. miereus is the constant presence in the latter of 5 or 5^ instead of 4 series of scales 

 above the lateral line. 



Gerres californiensis and G. harengulus are two species which agree in the number 



