Osteology of Caturus and Osteorachis. 385 



Appendicular Skeleton. 



Of the appendicular skeleton scarcely any parts are pre- 

 served, but the right post-temporal and supraclavicle are 

 worthy of note. The post-temporal (Pi. X, fig-. 1, p.t.) agrees 

 in general characters with thatof ^wza, exhibiting the down- 

 ward and forwardly directed process near the outer margin ; 

 but its hinder portion is relatively longer and narrower, with 

 an almost spatulate end. There is an irregular rugose and 

 tubercular ornament on its middle region. The supraclavicle 

 is truncated above, with a concave facette about half its width. 

 It is a gently arched laminar bone, about four times as deep 

 as its maximum width, which is at the upper end. There is 

 an irregular coarse rugosity on its exposed hinder half. 



III. OSTEOSACSIS UACROCEPHALUS, FROM THE LOWER LlAS 



OF Lyme Regis. 



The foregoing and other recent observations necessitate a 

 few supplementary remarks on the fine example of Osteo- 

 rachis from the Lower Lias of Lyme Regis originally 

 described by Davis under the nameof Heterolepidotus graiidis'^ . 

 This specimen has lately been acquired by the British Museum, 

 and its reference to the genus now under consideration can 

 thus be verified by direct comparison with the type specimens. 



The imperfect cranium in this unique fossil (Brit. Mus. 

 no. P. 7797) is exposed from above, but the rostral end is 

 wanting and the anterior half of the frontals is shown only in 

 impression. The whole is much fractured, and is merely of 

 interest as displaying the prominent tubercular ornament in 

 the hinder region and the extremely wavy suture between 

 the frontals where they begin to become smooth. The 

 squamosal is lost on the right side, so that the original figure 

 of Davis does not indicate the total width of the occiput. 

 The jaws and tacial bones are entirely wanting, and ttie 

 appearances described by Davis as " lower jaws 5 inches in 

 length " are better explained as a portion of clavicle crushed 

 upon the branchial apparatus. Nearly all the remains below 

 the skull, indeed, may be ascribed to the hyoid and branchial 

 arches. The branchial bars are delicate and covered with the 

 scatUred gill-rakers in the form of minute enamelled denticles. 

 These are especially interesting as being often clustered on 



* .1. W. Uavis, "On lleterolepidotHs (/randis, a Fos.<il Fish from the 

 Lias," Journ. Linn. Soc, Zool. vul. xviii. pp. 293-2!»8, pi. vii. (1885). 

 See also A. S. Woodward, " Un the Liaasic Fish, Odeorachis macru- 

 cephalus,'' Geol. Mag. [4] vol. ii. pp. 1^04-206, pi. vii. tig. 10 (l89o). 



