NOTHOSAURUS, stet.
Sp. Nothosaurus Miinster.—In fig. 69 is given an analysis of the chief charac ters as yet ascertained of the species which may be regarded as the type of its family ; by comparing this diagram with that of the Archegosaluruz (fig. 65), the advance in the orga nization of the aquatic reptiles will be readily traced and understood.
The skull is no longer de fended by a continuous covering of sculptured plate-bones ; the vacuities behind the orbits for the temporal muscles are large and widely open. These vacui ties are fenced externally by two long and slender horizontal bony bars ; the upper one is formed by the mastoid (fig. 69, ), and the post-frontal (22) ; the lower one by the malar (27), and squamosal (28) ; the latter answering to the true zygomatic arch in Mammals. The squa mosal abuts by its hinder. ex paraded end against the almost vertical tympanic pedicle, which gives attachment to the lower jaw. This shows the reptilian compound structure : 19 marks the surangular ele ment, 30 the angular one, 32 the dentary. In the side-view of the skull in fig. 69, 2Z is the premaxillary, 21 the maxillary, is the nasal—the cavity below being the nostril, io is the pre frontal—between which and 21 is the lacrymal, II the frontal above the orbit. The premaxillary teeth and corresponding premandibular ones are unusually long, strong, and sharp ; there are two similar teeth in each maxillary ; the remaining serial teeth are smaller, but equally acute. There are no teeth on the palate.
The almost entire and undisturbed vertebral column, from the muschelkalk of Bayreuth, figured by Von Meyer in pl. 23 of his work on muschelkalk Saurians, and attributed by him to Nothosaurus mirabilis, gives the earliest indication of that modification of the trunk-bones which reaches its maximum in the Plesiosaurus (fig. 71), in which it was first detected by the sagacity of Twenty of the anterior vertebrae of this series, in Notho saurus, which begins with the atlas, have the whole or part of the rib-pit situated on the centrum as in the first vertebra in fig. 69 ; the pit is wholly there on fourteen vertebrae ; it begins to ascend upon the neural arch in the fifteenth, as in the second vertebra, given in fig. 69, and is wholly placed there on the
twenty-first vertebra.
According, therefore, to the characters by which the writer has proposed t to distinguish the cervical from the dorsal vertebra?, Nothosaurus has twenty of the former. In the specimen referred to, nineteen consecutive vertebrae show the rib-pit supported wholly on an outstanding diapophysis from the neural arch, as in the third vertebra in fig. 69 ; these are to be reckoned therefore as dorsal vertebra'. In the cervical vertebrae the rib-pit is large, vertically reniform, not divided by a groove ; its circumference slightly projects in Notho saurus.
There is no clear evidence of any of the cervical ribs being terminally expanded and hatchet-shaped, as in Plesiosaurus; those of the back are vertically longer than in Plesiosaurus, and more convex.
In the sacral vertebrae, fourth in fig. 69, the rib-pits again begin to sink upon the centrum.
There are two distinct sacral vertebrae in Nothosaurus. They are known by their long, straight, terminally-bent, and convergent pleurapophyses, the first of which overlaps a little the second. To the convergent ends of these riblets, the ilium (fig. 69, 62., pl) was doubtless ligamentously affixed. In the first caudal vertebra the par- and di-apophyses stand out much farther than in the sacrum ; but rapidly shorten in the second and third caudals. The compound process in each supports a short stiliform straight riblet, as in the fifth figured vertebra (fig. 69) ; the anterior and succeeding caudals support luemal arches and spines, after the disappearance of the pleur apophyses. The hamal arch disappears in about the eighth vertebra from the end, and finally the arch. The terminal centrums are subelongate and subcompressed. Both Nothosaurus and Pistosaurus had abdominal ribs, of which the median piece (fig. 69, hs) was subsymmetrical, the two rays diverging at a very open angle, and terminating in a point or a fork ; the side-pieces (p) seem not to have been so numerous as in Plesiosaurus.