174 SUPPLEMENT TO THE 



as I am aware, exceeded some 3^ lines in length by about the same in breadth and 

 3 in depth ; whilst the Devonian Slcenidium areola is a much larger shell, sometimes- 

 exceeding 5 lines in length by 6 in breadth and 4 in depth. Skenidium Leicmi occurs 

 also in the condition of internal casts, and impressions of the exterior, in the Ludlow 

 Shales at the North Esk section in the Pentland Hills, near Edinburgh. 



77. Skenidium Lewisii, var. Woodlandiense, Bav. Sil. Sup., PI. XI, figs. 1, 2. 



In the Middle Llandovery, at Woodland Point, Girvan District, Ayrshire, occurs what 

 I take to be a large variety of Sketiidium Zeioisii. The specimens collected by Mrs. R. 

 Gray partake of all the essential characters of the Wenlock type, differing from it in size 

 only, being nearly twice as large, and in this particular intermediate between it and the 

 Sic. areola. Perhaps all three may be after all varieties of a single type, but of this 

 we have not at present any positive evidence. Two examples of the Woodland variety 

 measured, length 3, width 5 lines, and length 3, width 4, depth 2 lines. 



78. Skenidium Lewisii ?, var. Hughsii, Dav. Sil. Mon., p. 254, PI. XXXYIII, 



fig. 26. 



This may be another and still older variety of Skenidium Lcicisii, since it is found in the 

 Coniston Grit at Helmside Dent ; so that it is possible that the same species, under slight 

 variation in size, may have continued to be represented from the Caradoc up to the Middle 

 Devonian. 



79. Skenidium ?, Shallockiense, Bav. Sil. Sup., PI. XI, figs. 6, 7. 



Shell somewhat subpentagonal, slightly truncated in front, hinge-line straight and equal 

 to the greatest breadth of the shell, extremity acutely angular ; ventral valve pyramidal 

 with a longitudinal sinus extending from the extremity of the beak to the front ; area 

 large, triangular, slightly curved, fissure triangular ; surface ornamented with numerous 

 small ribs which radiate from the extremity of the beak to the margin. Dorsal valve 

 not known. 



Length 3^, breadth 6^ lines. 



Of this species I am acquainted with three ventral valves only, so that the identification. 



