Ch. XXYIL] LOWER LUDLOW SHALE. 555 



bites, agreeing specifically with those of the subjacent Wenlock lime- 

 stone, that it is scarcely distinguishable from it by its fossils alone. 

 Nevertheless, many of the organic remains are common to the Aymes- 

 try limestone and the Upper Ludlow, and several of these are not 

 found in the Wenlock.'* 



According to Mr. Lightbody, the Aymestry limestones should be 

 considered as subordinate to the Lower Ludlow shales next to be men- 

 tioned, as in some places these shales with their characteristic fossils 

 occur both above and below it.f 



b. Lower Ludlow Shale. — This mass is a dark gray argillaceous de- 

 posit, containing, among other fossils, many large chambered shells of 

 genera scarcely known in newer rocks, as the Phragmoceras of Brod- 

 erip, and the Trochoceras of Barrande (see figs. 628, 629). The latter 

 is partly straight and partly convoluted in a very flat spire. 



The Orthoceras Ludense (fig. 630), as well as the cephalopod last 

 mentioned, is almost peculiar to this member of the series. 



Tig. 629. 



*m&' 



Trochoceras (Lituites) giganteus, J. Sow. Fragment of Orthoceras Lud^nsi, J. Sow. 



Near Ludlow; also in the Aymestry and Leintwardine, Shror <st Ire. 



Wenlock limestones, i nat. size. 



A species of Graptolite, G. Ludensis, Murch. (fig. 640, p. 559), a 

 form of zoophyte or polyp which has not yet been met with in strata 

 above the Silurian, occurs plentifully in the Lower Ludlow. 



Starfish, as Sir K. Murchison points out, are by no means rare in 

 the Lower Ludlow rock. These fossils present us with new genera, 

 but they remind us of various living forms now found in our British 

 seas, both of the families Asteriadce and Ophiuridce. 



Oldest hioivn fossil fish. — In 1855, when the last edition of this 

 work was published, I was unable to cite any example of a fossil fish 

 older than the bone-bed of the Upper Ludlow, but in 1859, a specimen 

 of Pteraspis was found at Church Hill, near Leintwardine in Shrop- 

 shire, by Mr. J. E. Lee of Caerleon, F.G.S., in shale below the Aymes- 

 try limestone, associated with fossil shells of the Lower Ludlow forma- 

 tion — shells which differ considerably from those characterizing the 

 Upper Ludlow already described. 



The genus Pteraspis, as we have seen (p. 532), is regarded by Prof. 



* Murchison' s Siluria, p. 133. 



f Quart. Geol. Journ., vol. xix. p. 371, 1863. 



