220 ' MEMOIRS OF THE CARNEGIE MUSEUM 



EXPLANATION OF PLATES. 



(All the specimens figured in the Plates (XX I.-XXX.) are reproductions of photographs made 

 by the author, the material being in either his own private collection, or the collection of the 

 United States National Museum.) 



PLATE XXI. Fig. 1. Dorsal aspect of the pelvis of Plotus levaillanti. Adult. (Coll. U. S. 

 Nat. Museum No. 18,743.) Two of the pelvic ribs show upon the right side. 

 Somewhat reduced ; the mid-longitudinal line of this bone measures 9.5 cm. 

 not including the ossified anterior tendinal extensions. 



Fig. 2. Basal view of the skull of Phaethon cethereus, adult, mandible removed, 

 slightly reduced. Specimen in author's collection. From the island of Sail 

 Pedro Martis, Gulf of California. Collected in April, 1889. 



Fig. 3. Superior aspect of the skull of Phaethon Jlavirostris, adult. (Coll. U. 

 S. Nat. Musum No. 17,841.) Slightly reduced, the reduction being propor- 

 tionate in amount with the skull shown in Fig. 2. 



Fig. 4. Skeleton of left foot of Fregata aquila, adult. (Coll. U. S. Nat. 

 Museum, No. 18,485.) Somewhat reduced. Sheath left on midanterior toe 

 shows the " pectinated claw." 



Fig. 5. Ventral view of the sternum of Phaethon cethereus, adult (author's 

 collection). Very slightly reduced. Collected in April, 1889. San Pedro 

 Martis Isle, Gulf of California. The skull in Fig. 2 and this sternum are 

 from two different individuals. 



Fig. 6. Left lateral aspect of the trunk skeleton of Phaethon Jlavirostris, adult. 

 (Coll. U. S. Nat. Museum, No. 17,841.) Very slightly reduced. The skull 

 shown in Fig. 2 belonged to this skeleton, but the reduction in the former is 

 somewhat greater. 



PLATE XXII. Fig. 7. Right lateral view of the skull and mandible of Sula gossi, adult 

 female (author's collection). Very slightly enlarged. Mandible detached. 

 The superior mandible is tubular at the extremity and pervious at the 

 apex. Collected at San Pedro Martis Island, Gulf of California, 16 

 Oct., 1888. 



Fig. 8. Basal view of the skull of Sula gossi, adult female (author's collec- 

 tion). Very slightly reduced. Collected at same time and place as the speci- 

 men shown in Fig. 7. 



Fig. 9. Basal view of the skull of Sula Brewsteri. Same specimen as shown in 

 Fig. 7. Very slightly reduced. Left pterygoid bone dislocated inwards to 

 show the form of the corresponding quadrate. 



