2 



BRITISH FOSSILS. 



to the former genus. In tracing the gradation from the narrow 

 elongated form of the typical Ophiopsides to the shorter and thicker 

 proportions of the Pholidophori, the little fish described in the fol- 

 lowing paragraphs, occupies the extreme limit between the two 

 genera ; the transitional form of Ophiopsis penicillatus completing 

 the series of that genus. It must, nevertheless, be considered a true 

 Ophiopsis, since the characters of the dorsal fin and vertebral column 

 are in strict accordance with that genus, and are of greater value 

 than the more trivial features in which it resembles some species of 

 Pholidophorus. 



Description. — Ophiopsis breviceps is a small fusiform fish, mea- 

 suring 4 inches in length by I in depth. The head occupies only one 

 fourth of the entire length. The vertebral column extends in a direct 

 line from the head to the commencement of the caudal fin, without 

 any curvature in the thoracic and abdominal regions. The bones of 

 the head and gill-covers are ornamented with a pattern rather 

 coarser than is usual in so small a fish. The mouth is large, and well 

 furnished with small, conical, sharp teeth. The pectoral fins resemble 

 those of the Pholidophori. The ventral and anal fins are small, and 

 approximate to each other. The dorsal fin commences in advance 

 of the ventral fins, and extends beyond the insertion of the anal 

 fin. It contains nearly forty rays. The upper lobe of the tail is 

 larger than the lower one, and is invested with scales for some dis- 

 tance, giving a heterocerque character to the organ. The scales are 

 small and rhomboidal. The upper margins are concave, the lower 

 ones convex. The enamel appears thicker on the margins of the 

 scales, causing a slight depression of the central area. The posterior 

 edges are strongly serrated over the whole body. 



Affinities. — The generic afiinities have been already alluded to. 

 The species is very distinct from all with which I am acquainted. 



Locality. — Lowest beds of the Lower Purbecks in Weekly, or 

 Oakleigh quarry, near Tisbury. 



History. — The figures and description are taken from the speci- 

 mens in the collection of the Museum of Practical Geology, the only 

 ones I have seen of this species. 



Explanation of Plate. 



rig. 1. 2. The fish, natural size. 



Fig. 3. Scale, magnified. 



Fig. 4. Tail of a larger individual.* 



P. DE M. Grey Egerton. 



This may be Ophiopsis pemcilhtus. — Agassiz, Poiss. Foss., vol. ii. p. 290. 



