242 E. Ray Lankester — On a new Heterostracoiis Fish-shield. 



cuttle-fisli, or deep-sea sponges at pleasure, according to the fragment 

 chosen. 



Moreover, I must point out that Dr. Kunth fails to state the 

 evidence against him fairly. He speaks of my specimen of Pteraspis 

 with scales attached in series (now in the British Museum), figured 

 in pi. V. of the Paleeont. Soc. Monograph, as a " badly-preserved " 

 shield. It is not a matter of the slightest consequence whether it is 

 "badly" or "well" preserved, beyond this point — viz. the preser- 

 vation of a portion of the characteristic substance of the shield. He 

 also fails to mention — what I have very carefully pointed out and 

 figured (pi. vii.) — viz. that the striations of Scaphaspis Lloydii, 

 which occurs in the same horizon with Pteraspis rostratus, differ 

 invariably from those of its associate in width and shape, as also 

 most widely do those of Cyathaspis Banksii differ from those of 

 Scapliaspis truncatus. 



I now submit a description of a new form of Heterostracous shield, 

 which is distinctly intermediate in form between Scapliaspis and 

 Pteraspis ; more clearly so than is Cyathaspis. The specimen is 

 from the neighbourhood of Abergavenny, and is in the Grey Corn- 

 stone of that district. It has been kindly placed in my hands by 

 Dr. MacCullough. The bed in which it occurs has furnished also 

 shields of Scapliaspis Lloydii, Pteraspis rostratus, and Pteraspis 

 CroucMi in excellent preservation. (See Plate X.) 



If we were for a moment to accept Dr. Kunth's view of the rela- 

 tionship of the associated Scapliaspis and Pteraspis, what, we may 

 fairly ask, is to be done with this form ? There is no place left for 

 it — head, tail, and " Zwischen-sttick " being already engaged by the 

 fragment from the Potsdam railway-station. 



A comparison of the accompanying drawing (PI. X.) with the wood- 

 cuts taken from the Palaeontographical Society's Monograph in the 

 April Number of the Geological Magazine, shows that the new 

 shield has more of the general outline of Pteraspis than of Scapliaspis. 

 There is a well-marked somewhat tapering rostrum, at the margins 

 of which are found, one on either side, a pair of notches, agreeing in 

 position with the orbital perforations of Pteraspis. The shield 

 terminates posteriorly on either side in a sharply-turned angle, as in 

 Pteraspis, and in the middle line is produced into a spine. It differs, 

 however, essentially from Pteraspis in this fact, that there is no 

 emargination of separate pieces — ^rostrum, disc, orbito-marginal or 

 oornual elements, and spine. In Pteraspis, see Monograph (pi. vii., 

 figs. 8 and 9), such constituents of the shield are distinctly marked 

 off, apparently by lines of suture or anchylosis ; and in the young 

 condition such pieces, especially the disc, are to be found detached 

 from the other elements. In the new shield the test appears to be 

 one continuous calcification throughout, as in Scapliaspis. Hence the 

 generic term Holaspis — which I have found written on a slip of 

 paper, apparently by the late Mr. Salter, affixed to one half of the 

 specimen. Holaspis differs further from Pteraspis in the interesting 

 condition of the orbital notches. In Pteraspis the marginal apertures 

 in the anterior portion of the shield — whether justly entitled to the 



