CLUPEIFORMES 391 



meet below to form a ventral keel. The pelvics are very small. Both 

 epineurals and epipleurals are present. The air-bladder is partly cellular, 

 the pseudobranch and pyloric caeca have disappeared ; but most remarkable 

 of all is the retention of a distinct though rudimentary spiral valve in the 

 intestine (Fig. 77). 



Platinx, Ag. ; Eocene, Italy. Chiromystus, Cope ; Brazil ; Chiro- 

 centrites, Heckel ; Istria Cretaceous. Ichthyodectes, Portheus, Cope ; N. 

 America and Europe ; Cretaceous. Chirocentriis, Cuv. ; Indo - Pacific ; 

 and Lignite, Sumatra. 



Family PHRACTOLAEMIDAE. A small family founded for a single 

 highly specialised African genus. The head is very small and the 

 toothless jaws protractile, the mouth when at rest being folded back on 

 to the top of the snout. The nostril is single on each side, with a barbel 

 in front. The intestine is very long and convoluted. Phractolaemus 

 appears to be allied to the Osteoglossidae (Boulenger [42]), but it has lost 

 the symplectic, the myodome, and the postclavicle. The interoperculum is 

 enormous ; moreover, the parietals are widely separated by the frontals 

 meeting the supraoccipital. The caudal region is very short. 



Phractolaemus, Blgr. ; W. Africa. 



Family CLUPEIDAE. The Herrings form a large family already well 

 represented in Cretaceous times. On the whole, they are of a generalised 

 structure ; but the small parietals are separated by the prominent supra- 

 occipital (Fig. 381). A superior temporal fossa, between the frontal and 

 parietal, and a pre-epiotic fossa are characteristic of almost all Clupeid 

 skulls (Fig. 381, B). Prootic and pterotic bullae, in which is lodged the 

 diverticulum of the air-bladder, and an auditory fenestra are usually 

 present. The eye-muscle canal is generally open behind. The upper 

 jaw is of very variable structure ; one or two supramaxillae are usually 

 present ; teeth may be placed on both the premaxilla and maxilla 

 (Engraulis), or on the former only (Pellonula), or on neither (Chatoessus) ; 

 the maxilla may be large and firmly fixed to the premaxilla (Thris- 

 sopatrinae), or movably articulated to the ethmoid behind (Clupeinae). 

 In some the maxilla is prolonged backwards beyond the angle of the 

 mouth, a peculiarity which is carried to an extreme in Coilia. 



The number of branchiostegal rays varies from thirteen in Dussumieria 

 to four in CJianos ; and of pelvic lepidotrichia from eleven to six. The 

 hypural bones remain simple. There is a remarkable development of 

 intermuscular bones, epineurals, epipleurals, and adpleurals ; and usually 

 the pleural ribs are joined below by a series of median V-shaped scales 

 so as to form complete hoops ; similar dorsal ridge scales may be present. 

 The coracoids join to a ventral keel ; and the postclavicle is quite 

 peculiar in that it overlaps outside the clavicle. 



Caecal prolongations of the air-bladder rest against the auditory 

 fenestra, and the pneumatic duct opens into the stomach. In Clupea 

 the hinder end of the air-bladder opens directly to the exterior by a 

 pore on the left of the anus, a quite unique arrangement among fish 

 (Fig. 383). 



Chanos is the type of an aberrant sub-family, sometimes associated 

 with the Albulidae (A. S. Woodward [505]), in which the cranial fossae, 



