ADDENDA ET CORRIGENDA. 
533 
doubt from the specimens recorded below that the fish truly 
belongs to this Chondrostean family; a catalogue of the specimens 
in the Collection is therefore appended here. The upper lobe of 
the tail, the fin-supports, and the axial skeleton of the trunk still 
remain unknown ; but the demonstrated arrangement of the cheek- 
plates appears to suffice for determining the systematic position of 
the genus. 
Genus PKATYSIAGUM, Egerton. 
[Eigs. & Descript. Brit. Organic Remains, dec. xiii. (Mem. 
Geol. Surv. 1872), no. 6.] 
Trunk elongate-fusiform. Mandibular suspensorium oblique; 
dentition consisting of a series of large, well-spaced conical teeth, 
and numerous smaller teeth irregularly arranged and somewhat 
clustered; head and opercular bones externally tuberculated, 
clavicular bones partly rugose. Fins of moderate size, with 
numerous small fulcra, the rays broad, all much bifurcated and 
closely articulated distally. Pelvic fins short-based ; dorsal fin 
about as long as deep, arising opposite or nearly opposite the pelvic 
pair; [anal fin unknown] ; caudal fin deeply forked. Scales thin, 
small or of moderate size, and several ventral series very narrow ; 
ornament comprising feeble, slightly-radiating ridges towards the 
hinder margin, and sparsely scattered tubercles on the anterior 
portion. 
Platysiagum sclerocephalum, Egerton. 
1872. Plotysiayum sclerocephalum, Sir P. Egerton, loc. cit. no. 6, pi. vi. 
Type. Imperfect distorted fish ; British Museum. 
The type species attaining a length of about 0*6. Form and 
proportions unknown, but head with opercular apparatus large and 
its length much exceeding the maximum depth of the trunk. 
Tubercular ornament almost disappearing on the hinder portion of 
the operculum and suboperculum and on the branchiostegal rays, 
coarsest and partly replaced by rugae on the clavicular arch ; very 
fine tubercles also on the two foremost rays of the pectoral fin. 
Maximum depth of hinder expansion of maxilla equalling about 
one-third of the total length of the bone, and the dentigerous border 
slightly sinuous; teeth smooth; suboperculum much more than half 
as deep as the operculum. Pectoral fin with about 20, and pelvic 
fin with about 10 ra} T s, the latter half as deep as the former ; dorsal 
fin with at least 16 rays, arising opposite a point immediately be¬ 
hind the pelvic pair. Tuberculations on scales very sparse. 
Form. Sf Loc. Lower Lias : Dorsetshire. 
