Breadth of ring 



I 



u 



Breadth of foramen 



604 PEOCEEDINGS OF TITE GEOLOGICAL SOCIETY. [June 20, 



The vertebral characters are well marked. The vertebrae are thin 

 osseous rings slightly constricted in the middle ; the concavity of 

 both surfaces is shallow, and involves nearly the whole breadth. 

 The diameters are unequal, their difference ranging from one-fifth 

 to one- eighth of the longest measurement. 



The notochordal foramen is also not a complete circle ; its longest 

 and shortest diameters coincide with those of the vertebrae, of whose 

 area it occupies from one -fourth to a half. 



The extreme examples measured in tenths of an inch are as fol- 

 lows : — 



9 

 7 



25 

 21 



In the majority the length (or antero-posterior measurement) is 

 between two-tenths and three-tenths at all points ; but the deeper 

 examples show an inequality in this respect — the length at opposite 

 points of the ring varying considerably, as 2-5 to 2-25 in one case, 

 as 4- 75 to 3 inches in another. 



Straight bones, similar to the neural spines of Dendroptychius, 

 occur in the same slab ; they measure 2^ inches in length. Asso- 

 ciated with scales showing the above-nientioned characters, there is 

 in the Andersonian Museum, Glasgow, a pectoral arch with which 

 are connected several bones giving attachment to long undivided 

 fin-rays. 



Locality : English and Scottish fields, from the Coal-measures to 

 the Lower Limestones. 



Ehombopttchifs, Huxley. Mgs. 1, 2. 



These scales vary from cordate-ovate to rhombic : the length in 

 the former case exceeds the breadth ; in the latter the reverse holds. 

 In general symmetrical, the elongated scales sometimes show undue 

 prominence of one anterior angle. The free and overlapped surfaces 

 are nearly equal in the rhombic scales; but in the cycloidal the 

 former is much the smaller. In both forms the punctate free sur- 

 face is ornamented with coarse straight ridges which follow the out- 

 line of the sides, meeting at an angle posteriorly, and thus giving a 

 rhombic aspect to the scale. The intervals of these ridges are crossed, 

 chiefly near the margin, by finer radial ones. The pattern may lose 

 its regularity — only two or three marginal ridges being complete, and 

 the remaining surface set with irregular tubercles. This occurs in 

 those scales which most nearly resemble the rhombic scales oiMega- 

 lichtJiys ; but the resemblance stops here ; for though in some speci- 

 mens of Megalichthys the bony surface exposed by the absence or 

 non-development of the enamel shows irregular tuberculation, or 

 even a faintly rhombic pattern like that just described, the scales 

 presenting these characters have their anterior area bounded by 

 straight lines, and do not show the cycloid outHne of those of RJiom- 

 hoptycliius, those straight lines, however, which bound anteriorly 

 the free area beino^ common to both. The under surface is smooth : 



