FISHES OF THE GENUS ACENTROPHORUS. 



37 



as those of this fish are not well preserved in the Marl Slate ; on 

 the exposed side of a specimen they are nearly always variously 

 splintered at the hinder border, and it is usually impossible to find 

 a perfect scale. A single example in the Hancock Museum 

 retains undamaged scales, and in this example, as in some in the 

 British Museum (Smith Woodward, 1895, p. 54), the scales have 

 the hind margin entire or at the most slightly frilled. It is 

 therefore evident either that the denticulation is an inconstant 

 character or that more than one species is included under the 

 name glaphyrus. Against the latter possibility is the fact that 

 the two examples showing the clearest denticulation -are respec- 

 tiveljr among the deepest and the shallowest in body-form. In 

 any case the denticulated scales do not form a reliable or useful 

 specific distinction. Nevertheless, A . glaphyrus \& distinguishable 

 from A. varians by several well-marked characters. The caudal 

 fin in ^. glaphyrus is considei'ably longer and more deeply forked 

 (much like that of PalcBoniscus in fact, whereas in the later 

 species the tail is shaped as in Lepidotus) ; the fulcra on all the 



Text-figure 15. 



Aceutrophoms glaphyrus. Restoration. 

 Aboiit natural size. 



fins are much longer and slenderer, with freely-projecting needle- 

 like points ; the pectoral fin is set a little lower on the body and 

 its basal lobe is so shaped as to permit of its being turned down- 

 wards with the preaxial border in front ; in the skull the frontal 

 is wider anteriorly than in A. varians, and the maxilla is shorter 

 and stouter ; the lateral line is prominent externally; the inner 

 face of the scales is ridged and the articulating pegs are narrow 

 and finely pointed — the inner face of the scales, in fact, resembling 

 that of ^4. alius, and still more closely that of Pala-oniscus. 



A note seems called for regarding the puzzling second figure of 

 A. glaphyrus in King's monograph (1850, pi. 22. fig. 4). The 

 original specimen is in the Hancock Museum. Behind the 

 pectoral region it is particularly well preserved, but the head 

 (which appears very large and " Paleeoniscid " in the figure) is in 

 reality broken up, part of the area being occupied by a good 

 impression of the skull-roof. 



A fish found in the Trias of Ohicopee Falls, Mass., was 

 described by Newberry (1888, p. 69, pi. 19. figs. 3, 4) under the 



