256 Rev. J. H. Crawford on the 
forms a curve with the concavity forward. The articular 
surface is divided into two parts by a ridge which runs 
obliquely from its inner posterior angle to about the middle 
of its anterior border. The outer portion is considerably the 
larger and is concave from side to side and convex from before 
backwards; the inner is convex in both directions. 
It will be convenient to defer the comparison of the cranial 
structure of the Plesiosauria with that of other reptiles until 
the skulls in some of the other genera have been described, 
especially since very considerable differences exist between 
the short-snouted Plesiosaurs of the Lias and the later 
Pliosaurs. It may, however, be mentioned that these latter 
appear to approach the Triassic Nothosaurs more nearly in 
the structure of the palate than do the former. 
EXPLANATION OF PLATE XIII. 
Fig. 1. Dorsal surface of an imperfect skull of Peloneustes philarchus, 
(Seeley) (specimen 1). 
Fig. 2. Ventral surface of ditto (specimen 4). 
Fig. 3. Frontal region of ditto (part of specimen 2). 
f. Frontal. pf. Prefrontal. 
ju. Jugal. par.for. Parietal foramen. 
la, (?) Lachrymal. p.m. Premaxilla. 
mex. Maxilla. post.pal.vac. Posterior palatine va- 
na. Nasal (?). cuities. 
o. Ridge on pterygoid. g. Quadrate. 
oc.c. Occipital condyle. sup.orb. (?) Supraorbital. 
pal. Palatine. vo. Vomer. 
p.o. Postorbital. 
XXXVITL.—The Hydroids of St. Andrews Bay. By Rev. 
J. H. Crawrorp, F.L.8., St. Andrews Marine Laboratory. 
Since the first list of Hydroids was published in the Ann. & 
Mag. Nat. Hist. in 1874 (vol. xi.) by Prof. M‘Intosh * 
several additional species have been procured. 
During the present season, again, a few forms have been 
added to the local Hydroids, which seem to show that the bay 
is probably richer than has been supposed. Many of the 
Athecata are known to attach themselves by preference to the 
red seaweeds and to Zostera marina. Unfortunately the 
west rocks, where Delesserta sanguinea grows most luxu- 
* And also copied in ‘Invertebrate Marine Fauna and Fishes of 
St. Andews,’ 1875. 
