52 MATTHEW ON OEGANISMS 



striae on the difFercut plates. The rostrum and the lateral plates have about six ridgelets 

 to a millimetre, the dorsal scute about six aud two-thirds, and the ventral scute about 

 eight ; on both dorsal and ventral scutes the ridgelets are somewhat closer on the sides 

 than they are on the central part of the scute. The character and arrangement of these 

 little ridges can be seen on the enlarged figure of the rostrum and adjoining plates. (See 

 Plate IV, fig. 4.) 



Size. — Length of rostrum, 5 mm. ; width, 13 mm. Length of left cornua, 15 mm. ; 

 width, 5 mm. Length of right cornua, (part preserved) 11 mm.; width, 5 mm. Length 

 of the pari of the dorsal scute preserved, 14 mm. ; width, 20 mm. Length of the part of 

 the ventral scute preserved, 22 mm. ; width, 15 mni. 



Locality. — Cunningham Brook, Westfield, N.B., in a bed of black fissile shale, inter- 

 calated in heavy beds of dark grey siliceous shales. 



Horizon. — Div. £ of the Silurian Series. 



II. — Eelated Genera and Species. 



In considering the related forms of Pteraspidian fishes, none appear to correspond so 

 closely to this species as the genera Cyathaspis of Lankester and Palaeaspis of Claypole. 

 Except that in our genu.s the lateral plates are divided into two parts, and that no orbital 

 plates can be observed between the rostrum and the lateral plates, and that there is a 

 ventral scute, there appears to be little difference between the first-named genus and this 

 in the general arrangement of the covering plates of the body. 



In Prof Lankester's monograph of the fishes of the Old Eed Sandstone,' we appear 

 to have only one example properly referable to the genus Cyathaspis ; for although 

 C. Symondsi is described under this genus, it seems doubtful if it should be so placed, and 

 Prof. Lankester appears to have referred it here provisionally. The typical species, 

 C. Banksii, Huxley and Salter, is Silurian, and, as above remarked, possesses a set of plates 

 quite analagous to those of the Acadian fish. There is also on the central plate (" dorsal 

 scute ") a rhombic tubercle (see Plate IV, fig. 6), which holds the place of a similar pro- 

 jection on the shield of the Acadian fossil. (See Plate IV, figs. 1 c and 2.) In Prof. 

 Lankester's examples of C. Banksii the surface markings appear to have been obscure, 

 except on the rostral and lateral plates ; we do not know, therefore, how far the markings 

 on the main plates of these two fishes were alike, but on the rostral and lateral plates 

 they were similar. 



In the genus Pteraspis there is a general analogy of parts to those of the Acadian 

 genus, but the resemblance in details is not so close as that observable in Cyathaspis ; in 

 Pteraspis the rostrum is elongated, the lateral cornua appear to be anchylosed with the 

 l^lates behind them, and the triangular area in the front of the tubercule on the dorsal scute 

 in the former genus is wanting. There is, however, in this genus a small circular plate 

 on the axial line between the rostrum and the dorsal scute which appears to correspond to 

 the oval area on the dorsal scute in Diplaspis ; if such is the case, the triangular area of 

 the front of the dorsal scute in Diplaspis and Cyathaspis is suppressed in Pteraspis. Prof 



' Memoirs of the Palseontographical Societj', London, 1868. 



