204 A. Smith Woodward — On a Liassie Fish. 



II. — On the Liassio Fish Osteorachis macrocephalus. 



By Arthur Smith Woodward, F.L.S., F.G.S., 



Of the British Museum (Natural History). 



(PLATE VII,i Fig. 10.) 



AMOl^G the fishes of the Lower Lias of Lyme Hegis, Dorsetshire, 

 described by Egerton from imperfect evidence, is the genus 

 Osteorachis, with the single species, 0. macrocephalus? The original 

 description and figure are so unsatisfactory that nothing beyond the 

 name of the fish is quoted even in Zittel's " Handbuch " (vol. iii, 

 p. 230), while this bears an appended query; and the author's definition 

 of the genus is certainly much too vague to admit of any precise deter- 

 mination of its systematic relationships. Under these circumstances 

 it is of interest to return to a consideration of the fish in the light of 

 more recently discovered specimens, which seem to the present writer 

 to comprise not only examples of the trunk but also, at least, one 

 satisfactory head. 



The type specimen, now in the British Museum, is shown only in 

 a general way in Dinkel's drawing, and Egerton's description is far 

 from explanatory. It comprises the imperfect head with the greater 

 portion of the trunk obliquely crushed and exposed from below. 

 Eemains of a large gular plate appear between the fragments of the 

 smooth mandibular rami ; and there are clusters of small, remarkably 

 slender, hollow teeth. The premaxilla cannot be identified with 

 certainty, but one obscure portion of bone seems to show the bases of 

 a single close series of larger teeth ; another fragment, exposed from 

 its oral face, must have originally borne at least three series of the 

 typical small teeth. On one large expanded bone, which may be 

 entopterygoid, the teeth cover an extensive area and axe in part 

 merely fine granulations. The hyomandibular is well shown on one 

 side, but in Dinkel's drawing it is not distinguished from an adjoining 

 element which appears to be the displaced metapterygoid. The 

 process of the hyomandibular for the support of the operculum is 

 long, but its hinder end is connected with the upper and lower 

 extremities of the element by a thin lamina of bone. Behind the 

 hyomandibular, parts of the operculum and suboperculum are seen 

 from within. The vertebral centra are not "completely ossified," 

 but are represented merely by distinct hjq^oeentra and pleurocentra ; 

 their arches are obscurely indicated through the displaced squamation. 

 The tubercles on the scales are occasionally elongated, and on the 

 hinder portion of some of the flank-scales they are observed to pass 

 into transverse strise which terminate in feeble clenticulations. The 

 fins are too fragmentary for detailed description. 



Some further account of the characters of the trunk and fins of 

 Osteorachis is given by Egerton from another specimen, now in the 

 British Museum (No. P. 3655). The structure of the head, however, 

 has never been more precisely indicated. The opportunity is now 

 afforded to supply this deficiency by a fossil from the Lower Lias of 

 Lyme Eegis, preserved in the Oxford Museum. This is a skull, 



1 For this Plate (VII) see the April Number Geol. Mag. 



- Quart. Journ. Geol. Soc. vol. xxiv (1868), p. 500, and Figs, and Descript. 

 Brit. Organic Eemains, dec. xui (Mem. Geol. Surv. 1872), no. 5, pi. v. 



