Dr. A. H. Foord — AcantJionautilus, Carboniferous Limestone. 147 



only feebly ossified. All the centra are longer than deep and 

 a little constricted ; while some of them clearly exhibit the segmen- 

 tation into two parts already noted in the anterior caudal vertebrfe 

 of previously described specimens. The backwardly inclined short 

 neural spines are distinct, except in about six terminal vertebra3 ; 

 and there are traces of the slender chevron bones as far as the 

 thirteenth vertebra from the end. The soft tissues are indicated 

 by a brown stain, of which the border is very sharply defined below, 

 but less continuously observable above. At the thirtieth vertebra 

 from the end the depth between the two borders of the stain is only 

 0-008 m., while at the terminal vertebra the depth is 0-005 m. 

 Unless appearances are deceptive, and this is improbable, the tail of 

 Stereosternum must thus have been an excessively slender appendage, 

 without any dermal expansion at the end. 



A fragmentary detached maxilla, from the same limestone and the 

 same quarry as the type-specimens of Stereosternum, exliibits a few 

 very long and slender teeth, like those already observed by Cope in 

 this genus. This fossil is in the San Paulo Museum. 



It is also interesting to add that Dr. Derby has obtained a typictil 

 Labyririthodont tooth from a siliceous limestone at Conchas, which 

 is almost certainly on the same horizon as that at Limeira. In fact, 

 evidence is gradually accumulating to render it still moi'e certain 

 that the Karoo Series of South Africa is well represented by 

 homotaxial deposits in the south of Brazil and in parts of the 

 Argentine Eepublic. 



EXPLANATION OF PLATE Y. 



Stereostermim tumidmn. Cope ; photograph of skeleton, ahout one-half natural 

 size. Early Mesozoic : near Limeira, San Paulo, Brazil. [Original in Museum of 

 San Paulo, Brazil.] 



II. — On a New Genus and Species of NAUTiLus--Livi^ Shell 



(ACANTHONAUTILUS BISPINOSUs) FROM THE CARBONIFEROUS LIME- 

 STONE OF Ireland. 



By Arthur H. Foord, Ph.D., F.G.S. 

 (PLATE VI.) 



THE shell to which I have given the above name is at present 

 unique. It was found, a few years ago, in a quarry at Clane, 

 in the county of Kildare, where I had for some time been in search 

 of Cephalopod shells. It was associated with characteristic species 

 of Carboniferous Limestone fossils, among which the following 

 Nautiloid shells may be mentioned, viz. SoJenocheilus dorsalis, Phil.,^ 

 sp., Asymptoceras cydostomus, Phil., sp., A. Foordi, Hyatt, and an un-, 

 described species allied to the last-named one. The marginal spines,; 

 at first obscurely seen in the matrix, at once attracted attention ;• 

 and although one was broken off and lost in the quarry debris, 

 the other was fortunately found in the fragment of rock struck off 

 from the shell, and was then carefully developed and attached to 

 the latter. Naturall}^ very diligent search has been made since 

 its discovery, and a sharp look-out kept for any further specimens 

 of this interesting species, but so far without any result. 



