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Show 310 ON THE SKULL OF OSTEOGLOSSUM FORMOSUM. [Apr. 2, but, at the same time, it is equally clear that there can be no direct phylogenetic relation between the two genera. Hence the independent development of an essentially similar mechanism in two such widely distinct fishes can only be regarded as an interesting and striking example of parallelism in evolution. EXPLANATION OF PLATE XXII. [The figures are all of natural size.] Fig. 1.. Lateral view of the hinder part of the skull of Osteoglossum formosum showing the lateral and articular processes of the parasphenoid and the mesial cluster of parasphenoidal teeth. 2. Ventral view of the same structures. 3. Lateral view of the bones of the proximal portions of the mandibular and hyoid arches, including also the proximal part of the lower jaw, the hinder section of the maxilla, and the articular surface on the metapterygoid. The dotted line indicates the extent to which the mesopterygoid and pterygoid bones overlap the inner surfaces of the metapterygoid and quadrate respectively. The process of the hyomandibular (hym.1) has been partially removed. 4. Ventral view of the same structures, showing the two opposable series of mesopterygoid teeth, the parasphenoidal teeth, and the mode of articulation of the metapterygoid with the two lateral condyles furnished by the parasphenoid. 5. The oral surface of the " tongue," showing the three principal series of teeth, the attachments of the first three pairs of hypobranchial bones, and the second basibranchial element. 6. Similar view of the " tongue" of Lepidosteus osseus, showing the arrangement of the two rows of rugose plates, the attachment of the hypohyals, and the fiRresfte braesnibcrea Lnechtitaelr sc.a rtilage. [The lettering is uniform throughout.] an. ar. as. b.b.\ bo. d. eo. eo.1 f. h.b.\ h.hy. hym. hym} l.t. m.pg. m.pg.1 m.t. mt.a. Angular. Articular. Alisphenoid. b.b.2. First and second basi-branchials. Basioccipital. Dentary. Exoccipital. Lateral plate of exoccipital. Frontal. h.bf, h.bf First, second, and third hypobranchials. Hypohyal. Hyomandibular. Process of hyomandibular. Lateral "lingual" teeth. Mesopterygoid. Prolongation of mesopterygoid on the inner surface of metapterygoid. Mesial " lingual " teeth. Articular surface of metapterygoid. para-mt. pg. Metapterygoid. mx. Maxilla. op. Operculum. pg. Pterygoid. p.op. Preoperculum. pr.o. Prootic. ps. Parasphenoid. ps.a. Articular process of sphenoid. ps.l. Lateral or ascending process of parasphenoid. ps.t. Parasphenoidal teeth. pt.o. Pterotic. q. Quadrate. s.o. Supraoccipital. sp.o. Sphenotic. s.t. Supra-temporal. s.t.f. Supra-temporal fossa. sym. Symplectic. v. Vomer. |