444 Dt\ A. S. Woodicard — Ichthyosaurus shoiving Embryos. 



viviparous lizards '). All the embryos are of the same size, relatively 

 large, and w^ith the proportions of the skull similar to those of the 

 parent's skull. The snout in every case points forwards. The 

 embryonic skull is best displayed in an individual far forwards within 

 the ribs above the vertebral column, where it is shown in direct side- 

 view. The rostrum here is crushed on the heads of the ribs, and bears 

 the impress of the latter, indicating the soft nature of its bone-tissue. 

 Behind the skull is part of the vertebral column in position, with 

 some of the ribs, and apparently the ossified portions of the coracoids. 

 A second good embryonic skull occurs slightly further back just 

 below the . vertebras of the parent, and is interesting as displaying 

 the teeth in the form of thin, hollow cones. At the hinder end of its 

 mandible is seen the ossified shaft of a humerus. Below and in 

 front of this second specimen are three more imperfect embryonic 

 skulls, only partiallj'^ exposed, the lowest somewhat obscured by the 

 black stomach-contents. Behind the middle specimen there occurs 

 part of the vertebral column with ribs ; and some of the small 

 vertebral centra appear to exhibit the facettes for neural arches. 

 The sixth embryo is indicated only by short chains of biconcave 

 vertebral centra scattered in the region of the pelvis. The limbs 

 are not shown in any embryo within the body, but there is an 

 embryonic fore-paddle 0*036 m. in length near the displaced ribs 

 above the head. The bones in this paddle are not completely 

 ossified, but so far as preserved are in their natural position. The 

 radius is half as long as the ossified part of the humerus, whereas in 

 the adult paddle the same bono measures only one-third the length 

 of the humerus. The length of the best embryonic skull is about 

 0-19 m., while that of the skull of the parent is not more than 0-5 m. 

 The largest number of embryos hitherto observed in one individual 

 of Ichthyosaurus acutirostris (quadriscissiis) is seven ^ ; and it is 

 interesting to note that in each recorded case of more than one 

 contained embryo, the young are always directed with the snout 

 forwards. A single embryo in the middle of one specimen in the 

 Stuttgart Museum is also turned forwards; but in each known 

 instance in which the single embryo is so far back as the pelvis, the 

 snout is directed backwards.^ The specimens recently acquired by 

 the British Museum conform to this rule. 



EXPLANATION OF PLATE XXIV. 

 Fig. 1. — lehthyosmmts communis, Conybeare ; skeleton showing very small embryo 

 in the pelvic region. About one -fourteenth nat. size. Lower Lias : 

 Somersetshire. [Chaning Pearce Collection, British Museum, No. R. 3372.] 

 Fig. 2. — Ichthyosaurus actctirostris, Owen [quadriscissus, Quenstedt) ; skeleton 

 showing remains of six large embryos within the ribs. About one-fourteenth 

 nat. size. Upper Lias : Holzmaden, Wiirtemberg. [British Museum, 

 No. E. 3300.] 



^ F. E. Beddard, "Note on an apparently Abnormal Position of the ' Brephos' 

 within the Body of a ^kmk {Chalcides lineafus)" : Proc. Zool. Soc, 1904, vol. ii, 

 pp. 145-147, text-fig. 25. 



2 E. Fraas, op. cit. H. F. Osborn, " Ichthyosaurs " : Century Magazine, 

 vol. Ixix (1905), pp. 414-422, text-figs. 1-6. 



^ See Seeley and Fraas; also A. Gaudry, " Les Enchainements du Monde 

 Animal — Fossues Secondaires" (1890), p. 185, fig. 275. 



