from the Silurian of Girvan, Ayrshire. 355 



remote from its front edge ; apophyses widely separated ; shell not 

 covered by the mantle. 



HelminthocJiiton Griffithi of Salter is recorded in Griffith and. 

 M 'Coy's Synopsis of the Silurian Fossils of Ireland, Dublin, 1846, 

 and five figures are given (plate v. fig. 5a-e), and. in the Addenda, 

 p. 71, M'Coy gives a short account of the fossil, which he describes 

 as "Linear-oblong, smooth, carmate ; plates bent at alow angle, thin, 

 deeply emarginate behind ; no distinct lateral area ; cephalic plate 

 half-oval, longer than wide, marked with four or five faint radiations, 

 and a few lines of growth." 



M'Coy gives the locality as Coolin, Galway (in flaggy mudstone) 

 [Salter gives the locality as Cong, co. Galway]. Salter gives a 

 woodcut (on p. 49, op. cit.) ; it has the same subquadrate form as our 

 fossil, but does not display the same ornamentation as that from 

 Girvan. This may, however, be due to the nature of the matrix, 

 and the state of preservation of the fossil. 



In any case it would not be safe to refer the Girvan Chiton to 

 Salter's species from Galway, seeing they differ from one another 

 considerably in the form of the valves, which, in the Irish specimen, 

 are shorter and deeper than in that from Girvan. 



H. Griffithi is also destitute of ornamentation, or nearly so, whilst 

 the Girvan form is ornamented with both concentric and radiating 

 lines. 



In his paper on fossil Chitons, Prof de Koninck gives a list of all 

 the species of Palgeozoic Chitons known to him in 1857, which we 

 here subjoin : — 



Permian. 



Chiton Zoftusianus, King. (and Carboniferous ?) 

 ,, Hoivseanus, Kirkby. 



,, {?)cordatus, ,, (and Carboniferous). 



Chitonellus Hancockianus, Kirkby. 

 ,, distorlus, ,, 



,, antiquus, Howse. 



Cabboniferous Limestone. 



Chiton concentricus, De Kon. 

 ,, gemmatus, ,, 



var. mosensis, De Eyckh. 



Viseticola, , , 



legiacus, , , 



eburonicus, , , 



,, priscus, Miinster. 

 ,, nervicanus, De Eyckh. 

 ,, turnacianus, ,, 

 ,, Mempiscus, ,, 



,, {Chitonellus) cordifer, De Kon. 

 ,, thomondiensis, Baily. 

 ,, Burrowianus, Kirkby. 



[The following additional species of Chitons from British Carbon- 

 iferous rocks are recorded by Mr. K. Etheridge, jun., F.R.P.S.E., 

 Proceed. Nat. Hist. Soc. Glasgow, 1881, pp. 84-104, pi. i. and ii. 



Chiton Dalriensis, R. Etheridge, jun. 

 ,, Armstrongianus, R. Eth. jun. 



