206 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jail. 7, 



EXPLANATION OF PLATE V. 

 (The specimens are reversed in the lithograph.) 



Fig. 1. Rain-prints on rippled surface, with Annelide-burrows (-(^reni- 

 colites sparsus ; young) in the hollows of the ripple. 



From 

 Yearling 



Church 

 Stretton. 



2. Arenicolites sparsus (adult) ; on the upper surface of the slab. )■ Hill, 



3. Arenicolites sparsus (adult) ; "1 raised casts of the burrows, on 



4. Arenicolites sparsus (young) ; J the lower surface of the slabs. ^ 



5. Rippled surface. ] 



6. Rippled surface. > Waterfall, above Church Stretton. 



7. Rippled surface. J 



8. Surf-ripple on current-marks. "I 



9. Sun-cracked surface. I- Yearling Hill. 

 10. Rain-prints and sun-cracks. J 



4. 0?i some species of Acid aspis from the Lower Silurian Beds 

 of the South of Scotland. By Wyville Thomson, LL.D., 

 F.R.S.E., Prof. Geol. Queen's Coll. Belfast, &c. 



[Communicated by Sir R. L Murchison, F.G.S.] 



[Plate VL] 



Having occupied part of my leisure for the last year or two in 

 examining the fossils of the Silurian beds of the south of Ayrshire, 

 described by Sir Roderick Murchison in 1851, I have met with many 

 species and not a few generic types additional to those included in 

 Mr. Salter's list accompanying Sir R. Murchison' s paper on the 

 Silurian Rocks of the South of Scotland*. As most of the known 

 British species of the genus Acidaspis have either been already de- 

 scribed or are now in process of description, I take an opportunity 

 of adding the few new forms which have hitherto occurred during 

 the course of my investigations. 



The specimens are few, and in many cases fragmentary. The first 

 two species are an addition to a little group already represented 

 among our Lower Silurians by Acidaspis Jamesii and A. bispinosa. 

 The group is formed of minute species, usually rather meagrely or- 

 namented, and having a tendency to the fusion of the various pro- 

 minent parts of the head ; a tendency which reaches its maximum in 

 the subgenus Trapelocera, between which subgenus and Acidaspis 

 proper (represented by A. mira^ Barrande, and A. Brightii^ Murch.) 

 this group may be considered a link. 



Acidaspis Lalage, sp. nov. PL VL figs. 1-5. 



A. lata, ovata; capita brevi, transverse; glabella triangulari, utrinque 

 duobus lobis lateralibus ovatis, a lobo mediano cerviceque alto, et a 



* Quart. Journ. Geol. Soc.vol.vii. p. 137. I shall not enter into a consideration 

 of the detailed section of the district at present. Following Sir R. Murchison, I 

 regard the whole of the fossiliferous Girvan beds as belonging to the very top of the 

 Lower Silurians. The Pinwhapple flags, however, I consider to be the lowest of the 

 series, equivalent to the Upper Bala, and passing through the Mullock Hill sand- 

 stone and the Craighead limestone into the Saugh Hill sandstone = Upper Caradoc, 



