243 BEPORT— 1873. 



fossil specimens. It seems to have been at tlie postero-external angle of the 

 coracoid. 



Von Meyer and Burmeister have described the bone here named coracoid 

 as the scapula, and the scapula (or suprascapula) as the coracoid. 



The coracoid of Trcmatoscmrxis is known ; it closely resembles that of 

 Arclmjosaurus. A detached scapula of Pliolidcrpeton has also occurred. No 

 scapula or coracoid has been found in the other genera. The thoracic plates 

 of Mastodonscmrus, Tremafosaums, Archerjosaurus, Loxomma, Pholidogaster, 

 Pteroplax (^.') , Keraterpeton, and Urocordylits (?) are known; but none have 

 hitherto been discovered in any of the species which constitute the " Micro- 

 sauria " of Dr. Dawson. 



Pelvic Girdle. — Arcliegosatirus still remains the only source of exact 

 knowledge respecting the pelvis of the Labyrinthodouts. The ischia are 

 elongate, flattened bones, which meet along the middle line. Their antcro- 

 extemal angles are overlapped by the expanded ends of the hatched-shaped 

 ilia, while the straight shafts of these latter bones are coutiniied backwards, 

 outwards, and upwards. Similar, but larger, hatchet-shaped ilia occur in the 

 Newcastle coal-field. They may belong to Loxomma or Antliracosaurus. 

 The connexion of the ilium with the vertebral column appears to have been 

 very slight ; and there is no indication of specially modified sacral vertebras. 

 The pubis is straight, and has much of the form of the femur or humerus, 

 being narrowed at the middle and broad at each end. The situation and 

 composition of the acetabulum is unknown. 



It would be highly interesting to know that the ilium described and 

 figured by Professor Owen* was actually the ilium of Lahririniliodon pa- 

 cliygnathus, or of any other Labyrinthodont ; but the evidence derived from 

 the place of discovery is not cogent, and the bone is remarkably reptilian in 

 character. 



Bones of tlie Limhs. — In the Carboniferous Labyrinthodouts the bony 

 elements of the limbs of vertebrates higher than fishes appear in their most 

 generalized form. The manus and pes are pentadactyle, and there is but 

 little difierentiation of the digits. Each of the long bones has expanded ends, 

 and is contracted towards the middle of the shaft. In the Carboniferous 

 species the articulations seem to have been very lax. There are no articular 

 processes, condyles, cups or trochlese ; and the bones appear to have been 

 connected in the simplest way, by ligaments and integument. The long 

 bones of Hylonomus and some other " Microsauria " are tubular, and consist 

 of a uniform osseous crust, enclosing a central cavity, which in the living 

 animal was probably occupied by cartilage f. In several other Labyrinlho- 

 donts, however, of Carboniferous age, true cancellous tissue is present in the 

 long bones. 



If the limb-bones attribiited to Mastodonsaurus have been so determined 

 correctly, it woiild appear that in the Triassic Labj'rinthodonts the long 

 bones and phalanges were, as in the Carboniferous species, dilated at the 

 ends and contracted in the centre. There is no indication of bony epi- 

 physes ; and the muscular impressions are few and simple J. 



In all the species whose limbs are accurately known from their occur- 

 rence together in the same matrix and in something like the natural position, 

 the corresponding parts of the fore and hind limbs (c. g. the femur and hu- 



* Trans. Geol. Soc, 2nd scries, vol. \i. p. i533, t. slv. figs. 16, 17. 

 t A humerus of DmdrcriKton shows cancellous tissue towards the estremities (Daweon, 

 « Acadian Geology,' 2nd ed. p. 365). 



% Paliiontologie Wiirtembergs, t. iii. figs. 4-8. 



