68 Miscellaneous. 



The squamosal has an extraordinary development, and extends on 

 the parieto-quadrate arch, and on the inner side of the temporal 

 fossa on each side of the parietal. The parietal is not so far con- 

 cealed as in Ichthyosaurus, but its posterior lateral process may be 

 seen wedged in between the squamosal and the thin, plate-like 

 opisthotic, which lies external to the supraoccipital on each side. 

 The opisthotic is the parietal of Owen, and the parietal branch of 

 the squamosal is the mastoid of the same author. 



This branch in Ichthyosaurus and Lystrosaurus is continuous with 

 the zygomatic portion of the bone, though another element might 

 have been originally coossified with it. The posterior portion of the 

 squamosal is prolonged remarkably ; it is applied to the posterior 

 face of the quadratum, and extends to its articular extremity. The 

 quadratura is a small bone of a plate-like form, in contact with the 

 squamosal above and the (?) prootic inwardly and anteriorly. Supra- 

 stapedial not distingiiished. The parietal branch of the squamosal 

 sends down a columella to the pterygoid. The prootic is a distinct 

 though small bone, below and in front of the squamosal. The pre- 

 sphenoid is plate-like, and much as in the Crocodiha. 



Prof. Cope thought that the Anomodontia, one of the earliest 

 (Triassic) types of Eeptilia, are one of the best examples of a gene- 

 ralized group among the Yertebrata. Thus the structure of the 

 posterior part of the cranium Ls largely that of Ichthyopterygia, and 

 partially that of Lacertilia ; of the oral parts of the cranium, the 

 prootic and mandible, of Testudinata. The vertebral characters are 

 partly those of Ichthyopteiygia, and the sacrum and rib-articulations 

 those of Dinosauria. The peculiar prespheiioid is characteristic of 

 Crocodilia, and the osseous interorbital septum of Rhynchocephalia. 



The position of the posterior plate of the squamosal in Ichthyo- 

 pterygia and Anomodontia seemed conclusive as to the homology of 

 that element with the bone covering the cartilaginous quadratum in 

 Batrachia Anura, and the osseous quadratum in Urodela and Dipnoi, 

 called tympanique by Cuvier, and temporo-mastoidean by Duges. 

 This bone had been already homologized with the praBoperculum of 

 Teleostei by Huxley; and it is thought that its present determination 

 in the Eeptilia estabhshed the serial homology of the praeoperculum 

 of the fish with the squamosal plate of the mammal. — Proc. Amer. 

 Phil. Soc. vol. xi. No. 84. 



Oti the Embryology of Limulus polyphemus. 

 By A. S. Packakd, Jun. 



After a detailed description of the embryological history of the 

 Limidus, the author concludes that before hatching it strikingly re- 

 sembles Trinucleus and other Trilobites, a conclusion to which the 

 whole account points. The Trilobites are therefore lower than the 

 Xiphosura ; the two groups should, on embryonic and structural 

 grounds, be included perhaps in one order ; and the former should 

 therefore be removed from the neighbourhood of the Phyllopods 

 and placed immediately next to Xiphosura. The organization 



