134 
ACTIN OPTEET GTI. 
1854. EEchnodus conjluens, leiosomus, speciosus, J. Morris, ibid. pp. 316, 
317. 
1869. TEchmodus orbicularis, J. Morris, Geol. Mag. vol. vi. p. 337, pi. x. 
[Nearly complete fish.; W. H. Huddleston Coll.] 
1890. Dcipedius leiosomus, orbicularis , politus , Woodward & Sherborn, 
Catal. Brit. Foss. Vertebrata, pp. 58, 59. 
Type. Imperfect fish. 
The type species, attaining a length of about 04. Maximum 
depth of trunk about equal to its length (exclusive of the caudal 
fin) and four times as great as the depth of the caudal pedicle* 
Head with opercular apparatus occupying about one-quarter of the 
total length; the external bones in the adult ornamented with 
very coarse tuberculations, closely arranged, more or less flattened 
or even hollowed on the operculum, and often fused into short 
vermiculating ridges. Marginal teeth robust, partly unicuspid, 
partly bicuspid. Pelvic fins arising midway between the pectorals 
and the anal; dorsal fin with 30, and anal fin with 18 rays. Scales 
nearly smooth, with few minute transverse striae and sparse puucta- 
tions; the hinder border delicately serrated. 
The small specimens named Dapeclius leiosomus differ from the 
typical D. politus in their somewhat more elongated form and in 
the sparseness of their tubercular ornament; but they are proved 
to be immature by the non-fusion of the parietal, frontal, and 
squamosal bones. The Collection seems to exhibit every gradation 
between these fishes and the large specimens commonly named 
Tetragonolepis conjluens. 
Form, df Log. Lower Lias : Dorsetshire. 
All the following specimens were obtained from the Lower Lias 
of Lyme Begis, Dorsetshire :— 
P. 3555. Head of large individual, with pectoral fin and anterior 
abdominal scales; the type specimen of the so-called 
Tetragonolepis conjluens described and figured by Agassiz, 
loc. cit. Enniskillen Coll. 
P. 3550 a. Bemains of head and abdominal region of a similar fish. 
Enniskillen Coll. 
P. 3556. Imperfect fish 0*39 in length, with displaced facial bones 
and wanting the anal fin. The ornament upon the oper¬ 
cular and facial bones is relatively as coarse as in the 
preceding specimen, but there is less tendency towards the 
fusion of the tubercles. The tuberculations upon the dorsal 
ridge-scales and the adjoining series are to a considerable 
extent fused into longitudinal rugae. Enniskillen Coll * 
