LIASSIC FORMATIONS. 125 



7, PL XXXII, have borne the above specific name in the Public Gallery of the Depart- 

 ment of Geology for fifteen years. The description was reserved for the present Mono- 

 graph, and I regret the unavoidable circumstances which have delayed its communication 

 to the Palseontographical Society. 



Reckoning the lost terminal caudal vertebrae according to the guiding analogies I 

 estimate the total length of the animal to include four lengths of the skull. Of this part 

 the length of the rostral extension anterior to the orbit is four and a quarter times the 

 antero-posterior diameter of that cavity : and yet the orbit is relatively larger than in 

 Ichthyosaurus tenuirostris. 



The teeth correspond in size with the slenderness of their supporting jaws ; they are 

 of difficult detection ; the best preserved show crowns, as in fig. 3, PL XXVIII. With 

 sufficient magnifying power traces of longitudinal striae are discernible on the enamelled 

 crown ; the cemented base is as little tumid as in Ich. tenuirostris. In the relative 

 minuteness of the teeth of Ich. longirostris we may discern the transitional step to the 

 edentulous Ichthyosaurs described by Prof. Marsh. 1 



I conclude that the present, together with other long- and slender-jawed Fish-lizards, 

 may have preyed in a great degree upon the contemporary Cephalopods with internal 

 rudimental shells as well as on Fishes. The eye in Ich. longirostris is proportionately 

 large, like the orbit which the sclerotic circle almost occupies, suggestive of the nocturnal 

 habits of the species ; the plates seem to have been not fewer than sixteen in number. 

 The present species, like Ich. tenuirostris, is characterised by the large size of the 

 pectoral fin, and that of the ossicles representing the carpals and phalanges of its digits. 

 These, however, are limited in number, as in Ich. tenuirostris ; the three normal digits 

 (n, in, iv) are instructively conserved, though not terminally entire, in fig. 7, PL XXXII. 

 The supplementary ossicles here preserved are, situated as in the tenuirostral species, 

 along the ulnar margin, forming a sort of rudiment of the digit (v), which is normally 

 developed in Ich. communis and Ich. intermedins. 



The scapula, clavicle, and coracoid of the same side as the fin are definite, but 

 dislocated. The coracoid repeats the type of that of Ich. tenuirostris so far as having 

 the anterior notch the best marked, but the posterior one is more faintly indicated. 

 The anterior notch (PL XXXII, fig. 9) is placed further back, and becomes lateral 

 rather than anterior. The articular prominence is also nearer the hind border of the 

 lamelliform bone. 



The radius and radio-carpal bone are notched anteriorly, as in Ich. tenuirostris. 



The pelvic paddle has the same relative size as in that species, and the same 

 tridactyle structure. 



I reckon forty-eight vertebrae between the skull and pelvis ; fifty-two vertebrae can 

 be made out in the extent of the caudal region preserved ; to which may be added about 



1 " A New Order of Extinct Reptiles (Sauranodonta)," ' Amer. Journ. of Science and Arts,' vol. xvii, 

 Jan., 1879, p. 85. 



