MUSEUM OF COMPARATIVE ZOOLOGY. 



73 



orbito-nasal parallel with pleural 



Raja Icevis. 

 subpleurals partly obsolete 



Raja ocellata. 

 tubules with dicliotoraous branchlets ; 

 pleural tubules distant from lateral 

 and hinder margins ; 

 subpleural tubules massed in front 

 of head ; 

 subpleurals and suborbitals form- 

 ing a network ; 

 subrostral and nasal meeting 

 Disceus strongylopterus: 

 no subpleural network ; 

 no lateral tubules on sub- 

 pleural ; 

 subrostral and suborbital 

 meeting 



Potamotrygon tnotoro. 

 lateral tubules on subpleural ; 

 subrostral and suborbital 

 meeting 



Urolophus halleri. 

 subpleural and suborbital 

 meeting, very tortuous 

 Dasybatus tuberculatus. 

 subpleural and suborbital' 

 not tortuous ; 

 orbitonasal a mere point 

 Dasybatus dipterurus. 

 no lateral tubules on subpleu- 

 ral ; tubules massed in 

 front; 

 suborbital forming a series 

 of four incomplete areas' 

 Dasybatus nudus. 

 pleural tubules reaching outer pec- 

 toral angles ; 



areas included by pleurals wider 

 than long ; 

 lower pleurals emerge two sev- 

 enths way from the median 

 to tip of snout 



Pleroplatea valenciennii. 

 lower pleurals emerge two fifths 

 way from median to tip 



Pteroplatea marrnorata. 

 lower pleurals emerge half-way 

 from the median to the tip 



Pteroplatea hirundo. 

 pleural tubules reaching little, if any, 

 more than half-way to the outer 

 angle ; 

 laterals not united across the ver- 

 tebrae ; 

 anterior cephalic tubes reaching 

 forward from skull ; 

 subrostral and prenasalunited; 

 median transverse 



Myliobatis aquila. 

 median vertical 



Aetobatus narinari. 

 subrostral and prenasal not 

 united 



Myliobatis freminvillei. 

 anterior cephalic tubes not reach- 

 ing in advance of skull; 

 oral not crossing symphysis ; 

 no long tubules on the oc- 

 cipital 



Rhinoptera brasiliensis. 



oral crossing, symphysis ; 



long tubules on the occipital 



Rhinoptera jussieui. 



laterals united by tubes across the 



vertebrae Dicerobatus ol/eraii. 



DESCRIPTIONS. 

 Chimsera. 



Chimcera monstrosa (Plate II.) has open groovea throughout both corporal 

 and cephalic portions of the canal system. The delicate membranes of the 

 inner part of the furrows are protected bv closely set scales which overhang 

 from each edge. There are no tubules. On the snout the canals present a 



