Kinahan — Formation of Bock-basins. 489 



that they may be " gonophores," or " ovarian vesicles," at first 

 attached to the parent stem, but finally becoming free-swimming 

 ''zooids." Bodies somewhat similar to these have been described by 

 Prof. James Hall (Decade II. of the Geological Survey of Canada), 

 as occurring in the Quebec shales, in connexion with the stipe of 

 Graptolites Whitfieldi, a diprionidian form ; and these are regarded by 

 him as reproductive cells. 



If this conjecture as to the nature of these curious bodies (to 

 which the term " grapto-gonophores" might be applied) be correct, 

 then the Graptolitidce would have to be finally referred to the 

 Hydrozoa, and would find their nearest analogues in the Sertularidce, 

 from which, however, they would always be separated by sufiiciently 

 distinctive and definite characters. 



The facts, that no traces of a central axis have been preserved in 

 these bodies, and that they are not yet known to occur in other 

 localities, where graptolites abound, would militate somewhat against 

 this hypothesis ; but the first may be due to the soft nature of such 

 an axis, and the second may be referable to the attention of geolo- 

 gists not having been directed to them. 



Since the above was written, I have examined the graptolitic 

 shales of Dobb's Linn, Glenkiln, and Duifkinnel Burn in Dum- 

 friesshire, and I have found similar bodies present in all these 

 localities, though not in such plenty, nor so well preserved. 



EXPLANATION OP PLATE XVII. 



Fig. !. Ovarian vesicle or " graptogonophore of Graptolite (?)," half natural size. 

 la. the same magnified. 



2. Ovarian vesicles of graptolites (?), half natural size. 



3. Graptolites Sedgivichii with ovarian vesicle (.''), half natural size. 

 Za. the same magnified. 



4. " Graptogonophore" vertically compressed, half natural size. 

 4«. The same magnified. 



5. " Graptogonophores" vertically compressed, half natural size. 



IV. — On the Formation of the "Eock-basin" of Lough Coerib, 

 County Galway. 



By G. H. Kinahan, F.E.G.S.I., of the Geological Survey of Ireland. 

 (With two Lithographic Maps. Plates XVIII. and XIX.) 



LOUGH COEEIB is a long irregular lake of various widths, but 

 having a general bearing of about N.W. and S.E. Its N.W. 

 portion is in a granite and metamorphic rock country, while the rest 

 of it overlies Carboniferous rocks, principally limestone. The 

 northern portion is deep, the southern shallow, and through the 

 whole of it are scattered numerous islands which, in the former part, 

 are generally composed of Boulder-clay, while those in the latter 

 portion are nearly always rock. Its knoAvn natural outlets are two, 

 one being over the barrier of metamorphic rocks at Galway (u on 

 Map, PI. XIX), ^ and the other a subterranean passage south of Castle- 



^ The accompanying Map (PI. XVIII. and XIX.) is copied from the Index Ordnance 

 Map of the county Galway, and on it, copied from the Chart of Lough Corrib, are the 



