ICHTHYOPTERYGIA. 170 



FIG. 111. 

 DIAGRAM ILLUSTRATING THE PRINCIPAL CHARACTERS OF Ichthyosaurus. 



A, B, C, D. Ichthyosaurus longifrons ; skull from the lateral, superior, palatal, 

 and posterior aspects, wanting the anterior part of the rostrum, one-fifth 

 nat. size. L. Jurassic (U. Lias); Normandy, ag., angular; art., articular; 

 b.occ., basioccipital ; b.s., basisphenoid ; rf, dentary; ex.occ., exoccipital; 

 /.., foramen magnum; fr., frontal; i.pt., interpterygoid vacuity ; j, jugal; 

 la., lachrymal; mx., maxilla; na., nasal; nar., external narial opening; 

 occ.c., occipital condyle; op.o., opisthotic; pa., parietal; pas., para- 

 sphenoid; pin., pineal foramen; pi. , palatine; pmx., premaxilla; prf., pre- 

 frontal; pt. , pterygoid; pt.nar., posterior nares; ptf., postfrontal ; pto., 

 postorbital; q.j., quadrate- jugal ; qu., quadrate; s.ag., surangular; s.occ., 

 supraoccipital ; s.t., supratemporal (prosquamosal) ; x.t.f., supratemporal 

 vacuity; scl., sclerotic plates; spl., splenial; sq., squamosal; x, space for 

 ectopterygoid (?) ; v t vomer. (Restored from specimen in British Museum, 

 no. 33157.) 



E. Ichthyosaurus communis; upper tooth, showing extent of enamelled crown 

 and fluted base, one-sixth nat. size. L. Jurassic (L. Lias) ; Dorset. 



F. Ditto ; transverse section of base of tooth. Ibid. (After Owen.) 



0. Ichthyosaurus longifrons; atlas and axis, left lateral aspect, about one-third 

 nat. size. U. Lias; Normandy, b.occ., basioccipital condyle of skull; c 1 , 

 centrum of atlas ; c 2 , centrum of axis ; n l , paired neural arch of atlas ; 

 M-, single neural arch of axis; r, ribs; w, subvertebral wedge-bones (inter- 

 centra or hypocentra). (After Owen.) 



H. Ichthyosaurian dorsal vertebra and ribs, anterior aspect, much reduced. 

 L. Lias; Dorset, nbd., abdominal ribs; r, rib. (After Owen.) 



1, J, K. Ichthyosaurian vertebra from base of tail and two caudals, anterior 



aspect, much reduced. Ibid, ch., chevron bone; r, rib. (After Owen.) 



L. Vertical transverse section of Ichthyosaurian caudal vertebra, much 

 reduced. Ibid. 



M. Ichthyosaurus communis; pectoral arch, ventral aspect, much reduced. 

 Ibid, ac., glenoid cavity for humerus; cl., clavicle; co., coracoid; i.cl., 

 interclavicle (anterior transversely-extended portion covered by the cla- 

 vicles) ; sc., scapula ; .r, edges originally bordered by cartilage. (Restored 

 from specimens in British Museum.) 



N. Ichthyosaurus communi*; left pelvic arch, outer aspect, one-third nat. size. 

 Ibid. U., ilium; j*., ischium; pb., pubis. (From specimen in British 

 Museum, no. 41849.) 



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