694 



SILURIAN GRAPTOLITES. 



tubes, traversed by distant septa, and arranged for the greater part parallel to the axis, or 

 slightly diverging from it : surface fine net-work. 



This fossil resembles externally De Blainville's figure, Man. d'Actinol., PI. LXVI. f. 1, of 

 Verticillipora cretacea (De France), but no trace has been observed of the peculiar internal 

 structure represented by De Blainville in fig. 1 a. It has nevertheless been thought more 

 advisable to place the fossil in the genus Verticillipora than to make a new one. The spe- 

 cimens were found by Dr. Cook, of Tortworth. 



Formation and locality. Upper Silurian Rocks, {Ludlow and Wenlock, compressed) 

 Purton Passage. 

 Cnemidium, Goldfuss. 



Cnemidium tenue, sp. n. Lons. PI. 16 bis. f. 11, 11 a, 11 b. — 11 magnified twice, 11 a exhibits the 

 centre gravity and the horizontal tubes, 11 b surface pores magnified still larger. 

 C. mammillated or tubular, central gravity large, substance of the fossil thin, radiating hori- 

 zontal canals or pores distinct r tmd numerous. 

 Formation and locality, Wenlock Limestone, Dudley. 



Graptolites. 

 plate 26, figs. 1, 2, 3 and 4. 



These fossils have been alluded to as good tests of the age of the strata in which they occur, (pp. 

 206, 309, 326, 401.) It has further been shown, that they are usually found in deposits, which from 

 their structure were well suited to the habits of the family of "sea pens,'" of which they form a genus. 

 They were named Graptolites by Linnaeus, and have since been partially described under different 

 names by Wahlenberg, Schlotheim, Hisinger, Nillsson and Bronn. The Danish naturalist Dr. Beck, 

 who is preparing a monograph of them, has supplied me with the following sketch. From his re- 

 marks it appears that one of the species, very characteristic of the Upper Silurian Rocks, (PI. 26. f. 12.) 

 occurs abundantly in Norway and Sweden. Dr. Beck intended to name this species Graptolithus 

 virgulatus, but not yet having printed his monograph, he authorizes me to use any other term, and 

 therefore I adhere to the name of G. Ludensis, which was adopted before I received the description 

 of the learned Dane 1 , (see p. 206.) It does not, however, appear certain that there is any real 

 distinction between this fossil of the Ludlow Rocks and the Prionotus Sagittarius, Hisinger, (Or- 

 thoceratites serratus, Schlotheim). The fossil, fig. 3., is not adverted to by Dr. Beck. It seems 

 most to resemble Prionotus Folium, (Hisinger), but differs from that species in the number of fo- 

 liations, and I therefore venture to suggest the name of Graptolithus foliaceus. This species was 

 found in the calcareous flags of Meadow Town near Shelve, Salop (Llandeilo Flags). Fig. 4., of the 

 same plate, being unknown to Dr. Beck, he has, as above stated, named it after me. The Graptoli- 

 thus Murchisonii occurs in the Lower Silurian Rocks, and volcanic grits of the Llandrindod Hills, 

 Radnorshire, (p. 326.) 



These pen-like, serrated fossils have a great vertical range in the older or " Protozoic " rocks, 

 being found from the lower part of the Ludlow formation, down to very ancient beds in the Cam- 

 brian System, in which they were collected for example by Professor Sedgwick in Abereiddy Bay, 



1 Mr. Lyell, during a recent tour in Denmark, obligingly obtained for me the description of Dr. Beck. 



