482 Memoir Sears Foundation for Marine Research 



inence on either side providing support for anterior radial cartilages of cephalic fin. 

 Cephalic fin with 24—26 slender radial cartilages. Pelvis strongly arched with long 

 slender median process directed forward (Fig. 79 E).^^ 



Remarks. The most interesting anatomical feature peculiar to the mobulids is that 

 each of the inner branchial openings through which the pharynx connects with the 

 gill pouches is entirely surrounded, and thus guarded, by a single series of lamellae or 

 gill plates'* implanted on the visceral arches at right angles to the latter: one series on 

 the posterior face of the hyoid arch ; a series on each face of the first to fourth branchial 

 arches; and a series on the anterior face of the fifth arch. Their arrangement thus paral- 

 lels that of the gill filaments. 



These gill plates are thin, are either membranous or more or less horny, and have 

 cartilaginous basal supports. They are several times as long as high, the free margin 

 rising from the inner face of the gill arch toward the outer face, i.e., toward the gill folds 

 (Figs. iioD, 1 12 A), with the plates on the posterior face of each arch more or less 

 semilunar in lateral outline. There may be as many as 85-100 gill plates per arch in 

 Mobula, 130—140 in Manta at a breadth of 15 feet; undoubtedly there is a still larger 

 number in the adult Mantas. 



The free distal edge of each plate is expanded transversely in double-pinnate form. 

 In the genus Mobula the outer extremities of these lateral expansions of adjacent plates 

 are in the form of rounded lobes which continue separate one from another though 

 closely in contact (Fig. 1 10). But in Manta (Figs. 1 1 1, 112) they are rod-like, and those 

 of adjacent plates are fused at their tips in more or less zigzag pattern. Thus in Manta 

 they form a continuous grid or sieve on each of the faces (anterior and posterior) of 

 each of the gill-bearing arches," extending across the whole breadth of the zone oc- 

 cupied by the plates and around the entire length of each gill arch. With upwards of 

 130—140 plates on either gill-bearing face of each arch, and with each plate connected 

 with the neighboring plate on either hand by some 40—70 bars or more, the total 

 number of openings per arch in each of its branchial sieves is something like 7,000—9,000 

 on two-thirds grown specimens, doubtless many more on adults.*^ 



Each opening in the branchial sieve is partially subdivided by some 13—16 (or 

 more) round-tipped lobelets along the face toward the pharynx of each of the bars. 

 And the presence of many sharp conical denticles scattered irregularly over these 

 lobelets and over the inward- and outward-facing surfaces of the gill bars renders the 

 sieve still finer. 



Since the individual plates increase in height outward across each arch toward the 



59. For account of modifications of the branchial rays, see Garman (Mem. Harv. Mus. comp. Zool., 36, 1913: pi. 75 

 and expl.). 



60. Also termed prebranchial plates or prebranchial appendages. 



61. The structure of the branchial sieve has long been known for Mobula (p. 484, footnote 63), but to our knowledge 

 it has not been described previously for Manta. 



62. On our II foot 5 inch specimen of Manta there are 136 plates on the anterior face and 132 on the posterior face 

 of the first branchial arch. Each plate is connected with its neighbors on the anterior face by 43-46 crossbars along 

 the dorsal half of the arch and by 60-63 crossbars along the ventral half; by about 55-60 crossbars along the dorsal 

 half and by about 75 bars along the ventral half on the posterior face of the arch. 



