EXPLANATION OF PLATES. 761 



Fig. 4. Amphioxus lanceolatus, after JOHN MUELLER Ueber den Bauu. 

 die Lebenserscheinungen des Branchiostoma lubricum, Tab. I. 

 fig. 1 ; twice the natural size. 



Fig. 5. Heart of Squatina vulgaris, pp. 65, 66. B, ventricle ; c, mus- 

 cular appendage of the heart with three rows of valvular 

 projections; a, valves at the upper margin of the appendage. 

 See p. 60. 



Fig. 6. Head of Sphyra or Zygoma Blochii Cuv., p. 68, from Java; 

 one-fourth the natural size, seen obliquely from below; a, a, 

 the five branchial apertures on the right side ; b, b, the eyes ; 

 c, c, the nostrils. 



Fig. 7. Heart of Orthragoriscus mola, p. 78, half the natural size. 



A, auricle; B, ventricle laid open ; at the deep part of it is seen 

 the transverse opening of the auricle, provided with valves; 

 a, a, semilunar valves at the upper part of the heart (a, one of 

 the two small accessory valves) ; c, bulb of the aorta, formed of 

 elastic tissue. Compare p. 75. 



PLATE III. FISHES, continued and concluded. 



Fig. 1. Skeleton of the Perch, Perca fluviatilis, p. 200, reduced, after 

 CUVIEB et VALENCIENNES Hist. not. des Poiss. PI. i., as an ex- 

 ample of an Acantliopterygian. The anterior rays of the dorsal 

 fin P d, are spinous ; PC, is the caudal fin ; P a, the anal fin ; 

 pp, the pectoral fin; P v, the ventral fin. Compare pp. 16, 17. 



Figs. 2 and 3. Gills of the Lophobranchii, pp. 75, 76. 



Fig. 2. A. Head of Syngnathus acus, p. 77, seen from the left side ; 

 a, the small branchial aperture. Fig. 2, B, the same head from 

 below; on the right side the gill-cover has been Removed, and 

 there the clustered gills a are seen ; below them is a partition 

 which closes the branchial cavity behind ; behind this in the 

 middle is situated the heart b. Fig. 3 (copied from H. RATHKE 

 Untersuchungen iiber den Kiemenapparat, Taf. iv. fig. 2). A, a 

 gill magnified ; on it two rows of short gill-leaves may be seen ; 



B, one of these gill-leaves apart, more highly magnified. 



Fig. 4. Upper jaw of Diodon bicolor, n. p. 79, from a preparation 

 in the collection of comparative anatomy at Paris, to illus- 

 trate the characters of the Pectognathi, comp. p. 77 ; a, supe- 

 rior maxillary bone ; 6, intermaxillary bone ; c, rough surface 



