FISHERY BOARD FOR SCOTLAND. 



ON THE EdGS OF CERTAIN SKATES (RAIA). 



BY 



H. CHAS. WILLIAMSON, M.A., D.Sc, F.R.S.E., 

 Makine Laboratory, Aberdeen. 



(Plates I.-V.J 



The egg-cases or purses of the different species of Skates differ 

 markedly from one another. They have tests of a somewhat horny 

 nature, and enclose the yellow yolk (ovum) surrounded by the 

 translucent albumen (white yolk). 



Beard* described the purses of five species, viz., JRaia batis, clavata, 

 maculata, circularis, radiata. No figures of the purses accompanied 

 his paper. I have prepared drawings of the egg-cases of seven 

 species of skates. Most of the specimens Avere obtained at Aberdeen 

 Fishmarket by Mr. P. Jamieson, formerly attendant at the Laboratory. 



The purse of a skate is somewhat rectangular in shape. It has its 

 four angles produced into curved horns, which vary much in length 

 in the different species. The lateral borders are usually flattened 

 into a more or less broad margin. In circularis it is rounded. In 

 macrorhynchus it is moulded. 



Baia macrorhynchus, Raf. {Raia nidrosiensis, Collett). Jumbo 

 Skate (Aberdeen). — This species has the largest purse of the 

 collection. A drawing made from a dried example is shown in 

 natural size in fig. 7. It was not unlike a huge purse of Baia hatis, 

 but it had no side tendrils. Mr. Eunson presented two purses 

 which were taken out of a skate at Aberdeen in April. They were 

 about 10| to 11 inches (26-5-28 cm.) in total length. Measured 

 along the middle line they were 9y^ inches (24-3 cm.) long. In 

 extreme breadth they measured at the ends, in one case, 4^ and 5 

 inches (107 and 12-7 cm.) respectively, while the breadth across the 

 middle of the length was 5^ inches (14 cm.). In the case of the 

 second, the extreme breadths were, at the ends, 3|f and 4f inches 

 (10 and 11-7 cm,), and across the middle 5^ inches (13-9 cm.). The 

 lateral edge of the purse forms a high Ion efitudinal ridge. 



Baia batis, L. — This fish is known as Skate, Grey Skate, and Blue 

 Skate. Its purse is shown in natural size in fig. 2. It has attached 

 to either side of one end (the lower end, according to Beard) a long 

 golden tendril, composed of fine silken hairs entwined in a soft, rope- 

 like form. The egg-case, when taken from the skate, is of a light 

 amber colour. Its test is composed of two layers which separate 

 readily (fig. 1). The outer layer is of light amber colour, and is 



* Beard, J.— "On the Development of the Common Skate (fcaia batis)." 

 Three plate.s. Eighth Annual Report of the Fishery Board for Scotland, Part 

 III., for 1889. 1890. Pp. 300 et seq. 



Wt. 3377/8—500—7/1913. 



