THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE II. VOL. VIII. 



No. v.— MAY, 1881. 



0:RX(3-X1<TJ^1L, .A.I^TIOLE]S. 



I. — Note on a fine Head-shield of Zenaspis {Cephalaspis) 

 /S^LfrjET/, Egerton bf.= Cephalaspis ASTEROLEPiSjlS.AS.hY.Y. 



By the Editok. 



(PLATE VI.) 



OK our Plate is depicted the head-shield of the well-known Old 

 Eed Sandstone fish, Cephalaspis, the genus first described by 

 Agassiz in 1835, the species C. Salweyi, by Egerton in 1857, and 

 still later as C. asterolepis, by Harley in 1859. The specimen was 

 obtained by Mr. John Edward Lee, F.G.S., of Torquay, from the 

 " Cornstones," Old Eed Sandstone, Skerrid Vawr, near Abergavenny, 

 and is drawn about one-third less than the natural size. " Two 

 cornua were obtained by Dr. Mac Cullough from the same quarry at 

 Abergavenny, furnishing the evidence of these parts which are 

 wanting in Mr. Lee's specimen " (Lankester). 



At page 53 of Professor Lankester's Monograph of Old Eed Sand- 

 stone Fishes (Part I. CephalaspidEe, Pal. Soc. Mon., 1870) is given a 

 life-size outline woodcut of this specimen ; but the breadth seems 

 somewhat too wide in proportion to the length of the shield, which 

 in Mr. Lee's specimen is more pointed in front. 



Mr. Lankester observes {op. cit. p. 54), "Another specimen has 

 been recently obtained for the British Museum which is better than 

 that in the Geological Survey Museum drawn on pi. xii. fig. 2 ; or 

 than Mr. Salwey's specimen " (see pi. xii. fig. 6). 



These specimens seldom show the outer tuberculated layer, upon 

 the character of which the specific differences between C. Salweyi and 

 C. asterolepis have been founded. On some of these specimens a 

 few of the tubercles are left here and there, but as a rule they 

 merely show the beautiful stellate polygonal structure beneath the 

 outer layer. 



Prof. Lankester observes, "Sir Philip Egerton attached importance 

 to the great breadth between the eyes, but the size of the individual 

 and variations in j)ressure are liable to affect this chai'acter." He 

 adds, " After some hesitation I have decided to associate C. Salweyi 

 and C. asterolepis as one species, not being able, on careful examina- 

 tion, to find any character which should separate the large specimen 

 described by Dr. Harley from Sir Philip Egerton's original C. 

 Salweyi." 



Concerning the genus, Prof. Lankester proposes [op. cit. p. 55) 



DECADE II. — VOL. VIII.— NO. V. 13 



