1 8 The Irish Naturalist, 



DONAX VITTATUS, var. TRUNCATUS (Marshall, ms.). 



BY MISS AMY WARREN. 



Mr. Marshall, of Sevenoaks, Torquay, to whom I owe much 

 regarding shells, has drawn \\\y attention to a form oi Donax 

 vittatus that I have sent him, and which is unlike the English 

 form. He says : — " These Irish specimens partake of some of 

 the characters of the var. turgida, which is * larger, ventricose, 

 and longer,' but in addition the posterior end is abruptly 

 truncate instead of being obliquely so. It is in reality an 

 intermediate form between D. vittatus and D. truncuhis, 

 having the proportions of the latter, but the typical charac- 

 teristics of the former, to which it belongs without a doubt." 



In my district, Killala Ba}^ this truncated variety is the 

 prevailing form, and the type the rarit3^ I have some speci- 

 mens of D. vittatus from the North Bull, Dublin, and all 

 belong to the type. It would be interesting if collectors along 

 the coast would note where the truncated variety appears. 



Mr. Marshall adds that this form is peculiar to the south 

 and west of Ireland, and he has given it the M.S. name of var. 

 truncatus, the characters being : — ** Thick and solid, deeper or 

 longer from the beaks, ver}^ convex, posterior slope short and 

 abrupt. He adds, " the umbonal area inside the valves of all 

 these Irish specimens is curiously fretted with deep pit-marks 

 which may be caused by an internal parasite. Many j^ears 

 ago in dredging the variety nitida on the Doggerbank I 

 found that 50 per cent, of them contained a small parasitic 

 crab, and the presence of parasites may also account for the 

 convexity of both these varieties." 



Fig. I Fig. 2. 



In the accompanying drawing, kindly made by Dr. ScharfF, 

 fig. I represents a characteristic specimen of the new variety 

 gathered by me at Killala Bay ; while, added for sake of 

 comparison, is an example of the type from Torbay (fig. 2), 

 sent me by Mr. Marshall. 



