ON THE STOCKDALE SHALES. 725 



Tail very short and wide, apparently with two rings to the short 

 conical axis. 



This species is allied to A. setirostris, Ang., and A. JRouauIti, Barr. 

 From the former it differs in its greater width and smaller size ; 

 from the latter in the character of the glabella-furrows and its 

 broader axis. Ampyx parvulus, Forbes, has many differences from 

 our form. 



Hor. ^ Log. Zone of Ampyx aloniensis, Skelgill and Browgill. 



Pboetus bkachyptgfs, n. sp. (PI. XVI. figs. 18, 19.) 



Length | inch, width i inch. 



Head ^ length of the Avhole creature. Glabella parabolic, with 

 two small circumscribed basal lobes. 



Body f length of the animal, 8 segments. Axis wide, rather flat, 

 with tuberculate extremities to the rings. Pleurae slender, strongly 

 grooved. 



Tail three times as broad as long. Axis tapering rapidly, and 

 extending two thirds the length of the tail, with 2-3 conspicuous 

 rings. Limb gently rounded, marked with three or four prominent 

 furrows. 



AVe have found two nearly complete specimens of this minute 

 form, which, though indifferently preserved, are quite unlike any 

 other form of Proetus which we know. The breadth of the whole 

 creature, the width of the axis, and the short broad tail are very 

 distinctive features. Isolated tails, apparently referable to this 

 species, are tolerably abundant. 



Hor. Sf Log. JSTot uncommon in the Ampyx-dloniensis zone of 

 Skelgill ; one specimen in the same zone of Pull Beck, near Am- 

 bleside. 



Ateypa plexuosa, n. sp. (PI. XYI. figs. 20, 20 a, 20 6.) 



Shell heart-shaped, with a fairly deep sinus. 



Yentral valve with a small, prominent, pointed beak ; sinus deep, 

 with a short tongue-shaped extension, and marked by eight pro- 

 minent, longitudinal ribs. Ribs less strongly marked on the convex 

 portions of the valve. About 14 rather prominent, transverse laminae 

 of growth. 



Dorsal valve with a very elevated mesial fold, the longitudinal 

 ribs and transverse laminae well developed over the whole of the 

 surface. 



Length | inch, width | inch, depth | inch. 



This species is intermediate in character between A. imhricata, 

 Sow., and A. altijugata, Lindstr. The sinus is narrower and deeper 

 than in the former species, but wider and shallower than in the 

 latter, from which it also differs by the possession of more strongly 

 developed transverse laminae of growth. 



Hor. Sf Log. Tolerably abundant in the Atrypa-fleoouosa zone of 

 the Lower Skelgill Beds, at Skelgill. 



