108 ON A WHITE BKEAM WITHOUT PELVIC FINS. [Jail. 20, 



4. On a Specimen of the White Bream {Abramis blicca, 

 Bloch) without Pelvic Fins. By H. H. BrindleYj M.A., 



St. John^s College^ Cambridge. 



[Eeceived January 3, 1891.] 

 (Plate X.) 



The fish forming the subject of this communication was obtained 

 from the Cam last August. It is a specimen of Abramis bliccu, Bl., 

 of which the commonest Enghsh name, the " White Bream," distin- 

 guishes the species from the Common or Yellow Bream {A. brama). 

 The former fish is described by Jenyns ^ as " very common in the 

 Cam " and as the " Breamflat " of the fen fishermen. The specimen 

 exhibits all the appropriate specific characters except as regards the 

 pelvic fins, which are altogether absent. A normal example of the 

 species was captured at the same place and during the same hour, 

 and for the sake of comparison an outline of it is given below the 

 figure of the abnormal fish. 



In the normal example the ventral surface from below the posterior 

 edge of the operculum to the origin of the pelvic fins is flattened and 

 is covered by four rows of scales, the scales of the two outer rows 

 having their outer edges bent upwards to interlock with the scales 

 of the lowest, rows of the sides of the body and so round off the 

 sides of the A^entral surface. Posteriorly to the pelvic fins the ventral 

 surface suddenly becomes sharp or rather ceases to be present, the 

 ventral edges of the scales in the lowest rows of the sides of the body 

 meeting in the ventral hne. 



This ventral compression of the body into an edge behind the 

 pelvic fins is a generic character ^. 



The above are also features of the abnormal example, subject to 

 the following modification at the proper place of origin of the pelvic 

 fins. The four last scales of each row of the posterior end of the 

 flattened portion of the ventral surface are of about the same size 

 and shape as the antecedent scales, but overlap each other much more 

 than the latter, viz. to the extent of about two-thirds of their 

 individual areas. These scales are, however, arranged regularly and 

 cover completely the proper place of origin of the absent fins. 



Dissection of the body-wall in this region, by stripping off the 

 different layers one by one, revealed no irregularity of arrangement, 

 the myocommas meeting in the ventral line in the same manner as 

 in the rest of the region between the pectoral and anal fins. 



On macerating the muscles, no trace of a pelvic girdle was found. 



The case is therefore one of entire absence of the pelvic girdle and 

 appendages, their presence normally not being suggested by any 

 rudiments. That the defect is congenital and not the result of 

 accidental injury, which would be unlikely on other grounds, is 

 indicated by the absence of any external mark or scar and the 

 complete regularity in the musculature. 



1 L. Jenyns, ' Manual of British Vertebrale Animals,' 1825. 



- A. Giinther, • Catalogue of Fishes in Eritish Museum,' vol. vii. p. oUO. 



