1862.] MORBIS AND BOBEKTS CAEBONIPEROUS LIMESTONE. 103 



On a New Species of Pterichthys (Pterichthys macrocephalfs, 

 Egerton), /rom the Yellow Sandstone of Parlow, Co. Salop. By 

 Sir Philip de Malpas Grey Egerton, Bart., M.P., F.R.S., 

 P.G.S., &c, 



[Plate III. Figs, 7, 8, 9.] 



The specimen oi Pterichthys discovered by Mr. Baxter, F.G.S., in the 

 yellow sandstone of Parlow is the smallest example of the genus 

 which has come under my notice. Its total length, from the anterior 

 margin of the head to the termination of the dorsal shield, is exactly 

 one inch, of which the head occupies four- tenths. The breadth of 

 the shield is half an inch. The fish reclines on the ventral plates, 

 thus presenting to view the upper surface of the body. The tail and 

 left pectoral appendage are deficient; but the right arm is pre- 

 served, and measures eight-tenths of an inch in length, or two-tenths 

 more than the carapace. See woodcut, fig. 1, and PI. III. fig. 7. 



On comparing these dimensions with 

 those of the other members of the genus, Pig. 1. — Outline of Mr. 

 it appears that, although the small size of Baxter^s Specimen of 

 the body suggests a resemblance to the Pterichthys macro- 

 PterichtJiys Milleri of Cromarty, yet the cephalus from Far- 

 disproportionate length of the pectoral ap- low. (See PI. III. 

 pendages (a feature of safe guidance in dis- fig. 7.) 

 criminating the species) assimilates it more 

 closely to Pterichthys hydrophilus (Pam- 

 phr actus of Agassiz) found in the yellow 

 sandstone of Dura Den in Scotland. It 

 differs, however, remarkably from this 

 species in the large proportionate size of 

 the head. The breadth of this member 

 in the Parlow species is just commensurate 

 with its leugth, whereas in Pterichthys 



hydrophilus it is one-third greater. The form of the head is also 

 very diff'erent in the two species ; the outline in the former is nearly 

 circular, whereas in the latter it is subtriangular, broad at the base, 

 and contracting towards the snout. 



The length of the pectoral oars in the Pterichthys of Dura Den 

 exceeds considerably that of these organs in any other species, being 

 equal to that of the dorsal shield ; but the English Pterichthys (the 

 only one yet discovered on this side the Border) transcends in this 

 respect that of Dura Den as much as the latter outstrips its con- 

 geners ; for the arms project one-fourth beyond the posterior margin 

 of the carapace. The plates of the cranium are not sufficiently per- 

 fect for description. 



I may here remark that a specimen recently acquired by the Mu- 

 seum of Practical Geology, from the Dura Den deposits, fully bears 

 out the opinion advanced by the late Hugh Miller and myself in 

 1848, as to the identity of the genera Pterichthys and Pamphractus. 



Since the foregoing description of the solitary specimen of Pter- 



