﻿24 ME. E. S. C0BB0LD ON TRILOBITES FROM [Feb. I9IO, 



figures and to his quotation of the original description of this 

 species. 



There is but one point that I have not identified. Shaler & 

 Foerste say that 'the most marked feature of the fixed cheeks is 

 the existence of a depression on their postero-lateral outline.' 

 Unless this be a reference to the wide postero-lateral groove, which 

 expands outwards, this feature is not present in the Comley 

 specimens. 



The most marked feature about these fixed cheeks is their 

 triangular aspect, as viewed from above. The two cheeks, taken 

 together, form a square elevated area set diagonally upon the 

 somewhat quadrate cranidium ; this feature comes out almost too 

 strongly in my figures. 



The specimens figured [405, 406, 576] do not show another 

 feature mentioned by the authors of the species. After referring 

 to the expanded ' anterior border/* ihey say that ' near the lateral 

 margins of the border, or rather near the facial suture, there are 

 sometimes two or three low tubercles visible.' One of the Comley 

 specimens (a very friable internal cast) exhibited similar tubercles 

 when first found, and was mistaken for a head-shield of Microdiscus 

 lielena, Wale, until the eye-lobe was exposed by removal of the soft- 

 matrix. The enlarged base of the combined glabella and occipital 

 ring lent colour to the illusion. 



The Comley specimens are about 2 millimetres long ; in the 

 original description the head is said to be ' small, often minute, in 

 the largest specimen 4 mm. long, usually 2-Q mm.' 



Locality and horizon. — Comley, from the Olenellus Lime- 

 stone, at the excavation 200 yards south of the quarry, and also in 

 the Dairy Hill excavation. It is plentiful. 



Ptychoparta (?) annio, sp. nov. (PI. Ill, figs. 5-8.) 



Four incomplete head-shields [401, 402, 403, 404] form the only 

 material available for description, but the features are so well 

 marked that the specimens seem worthy of specific designation. 

 The generic reference is quite provisional. 



Cranidium : Size — minute : length = about 2^ millimetres. 



General form. — Irregularly pentagonal; proportion of length 

 to width = 3:4. 



General convexity. — While the features are all in themselves 

 very convex, the general level of the head-shield is nearly horizontal, 

 but the sides appear to be much depressed. 



Glabella. — Strongly convex; distinct from the occipital ring ; 

 parabolic; almost pyriform in the cast, see specimen [401] (PI. Ill, 

 fig. 7) ; most elevated near the posterior end ; very depressed 

 anteriorly, as though it had been pressed down into the head-shield ; 

 without furrows ; about three-fifths of the total length of the head- 

 shield. 



Occipital furrow. — Entire; strongly impressed at the sides, 

 less so in the middle. 



