44 Oorrespondence—Ur. R. Lyjddeker ; Prof. T. G. Bonney. 
CORRESPONDENCE. 
IOHTHYOSAURUS ACUTIROSTRIS, ZETLANDICUS, & LONGIFRONS. 
Sir, —On page 313 of the Grotocicat Magazine, Dee. III. Vol. 
V. 1888, I stated that I was “disposed to unite both Ichthyosaurus 
Zetlandicus and I. longifrons with I. acutirostris. Since that passage was 
written Prof. Karl von Zittel has been good enough to send me a figure 
of an entire skull of an Ichthyosaurus from the Upper Lias of Curcy, 
evidently belonging to I. longifrons, which I consider inseparable 
from J. Zetlandicus. This specimen differs, however, from I. acuti- 
rostvis in its perfectly straight rostrum; and we have, therefore, a 
character which (if not merely sexual) will afford a valid distinction 
between the two forms. If I. quadriscissus of Quenstedt be identical 
with IL. acutirostris, the name FI. Zetlandiecus, as earlier than JI. longi- 
Jrons, should be adopted for the straight-beaked form. 
November 17th, 1888. k. LypEKKER. 
THE SERPENTINE OF THE LIZARD. 
Str,—There are two slight errors in Mr. Somervail’s paper “ On 
a Remarkable Dyke in the Serpentine of the Lizard” (p. 558 of last 
volume), which may mislead readers. They are contained in one 
sentence, “The dyke forms a portion of the ‘granulitic group’ of 
Prof. Bonney, which is now known to be of igneous origin.” (1) I 
have never placed any of the rocks near Pentreath Beach in my 
‘“‘granulitic group,” but speak of them more than once as belonging 
to the “hornblende schists.” (2) For ‘which is now known to be” 
read ‘which is now known to include some rocks.” ‘The origin of 
the distinctly ‘banded gneissic” portion, like that of the banded 
hornblende schists, cannot be said to be yet known to any one, unless 
Mr. Somervail has been honoured with a special revelation on the 
subject. Most persons who have particularly worked at questions 
of this kind consider the origin of these rocks a very difficult and as 
yet unsolved problem. ‘The speculations as to the origin and 
relations of the Lizard rocks, with which Mr. Somervail has favoured 
us, will no doubt meet with the attention which they deserve, regard 
being had to the wide experience of their author and his intimate 
knowledge of rock-structures. T. G. Bonney. 
THE GENUS ASCOCERAS. 
Sir,—The figure which Prof. Lindstrom gives in the December 
Number,’ of an Ascoceras from the Island of Gothland is a very 
instructive one—as it supplies some of the earlier septa which have 
hitherto been wanting and gives a final proof of their existence. 
It is thus completely confirmatory of the description of the genus 
which I gave on p. 61 of my British Fossil Cephalopoda. At the 
time of writing I was obliged to say “the earlier part is unknown” 
—which still remains partially true—since only three chambers of 
1 Grou. Maa. 1888, Dec. III. Vol. V. p. 583, Woodcut. 
