20 SHOULDER-GIRDLE AND BREAST-BONE. 



the preopercular nature of P. o. ; it is the suboperculum, which may be seen running up in 

 front of the operculum in Polyptcrus (op. cit., Rg. 17, S.op.); and in Lepidosteus (see Huxley 

 and Hawkins's 'Atlas/ plate 5, fig. 3, S. op.). In the left-hand figure the bone which comes 

 close behind the mandibular ramus is labelled S. op., or suboperculum ; but if the reader will 

 again refer to the figure of the Lepidosteus in the ' Atlas,' he will see that the " inter-opercular" 

 bone, which in all Osseous Fishes is tied by a strong ligament to the angle of the lower jaw, is a 

 large, long, ganoid bone, lying at the precise distance behind the angle of the lower jaw which 

 is given in the diagram of Glyptolatmus. If the "jugulars," J 1 and /2, were to send inwards 

 and upwards ossified aponeurotic plates, these would answer to the " splenial " and coronoid 

 plates that lie on the inside of " Meckel's cartilage" in Birds, Reptiles, and Sauroid Fishes. The 

 ganoid plates indicated by M. H. in the diagram are the dentaries ; and the symmetrical plates 

 which grow towards each other behind the great jugulars (Pet. 1 and 2) answer to the " inter- 

 clavicles" and lower "post-clavicles." The former are lettered C' in fig. 17, p. 22, in the 

 Polyptcrus in that oft-quoted memoir ; the latter have their counterparts in the Herring. (See 

 Plate II, fig. 6, p. cl. 3. Also represented in the lower half of the second infero-lateral plate of 

 Callichthys, Plate I, fig. 9, p. cl.) 



Example 2. Osteolepis. 



The restoration of Osteolepis, which is given (from Pander) in the same memoir (p. 11, 

 fig. 8), shows a " post-temporal" scarcely larger than the " supra-temporals," which are seen 

 running from the post-temporal to the orbit ; the front bone of that series articulates with the 

 last suborbital it is the post-orbital. Below the "post-temporal" is an enormous " supra- 

 clavicle /' below it an almost equally large " clavicle ;" and below that, and behind the jugular 

 plate, we see the " inter-clavicle." The fringed and elongated pectoral fin is seen emerging 

 from its hidden root behind the junction of the clavicle and inter-clavicle : that root, the 

 Shoulder-girdle moiety, or " coraco-scapular cartilage," was probably never ossified. 



PISCES DIPNOI. 



* 



Example. Lepidosiren annectens, Owen. 



For Professor Owen's descriptions of the anatomy and relationships of this unique type 

 of Fish, I refer the reader to the following works, ' Proc. Linn. Soc.', August, 1838, and April, 

 1839 j ' Ann. of Nat. Hist./ 1839, iii, p. 265 ; ' Rev. Zool./ 1839, p. 190 ; ' Linn. Trans./ xviii, 

 p. 237; ' Ann. and Mag. Nat. Hist./ 1841, vii, p. 358; 'Lect. Comp. Anat./ 1846, vol. ii, 

 pp. 7884; 'Nature of Limbs/ 1849, p. 92; 'Osteol. Catal. Mus. Coll. Surg./ 1853, vol. i, 

 Nos. 380, 381, pp. 85 89. For Professor Huxley's account of the affinities of Lepidosiren 

 the reader must consult his ' Memoir on the Ganoids/ p. 26. 



My dissections of the Shoulder-girdle of this fish are portrayed in Plate II, figs. 1 3 ; the 

 figures represent the parts as magnified three diameters, and the specimen (the gift of Mr. 

 Bartlett) was half-grown. 



