78 



Infraorbital 4 (Fig.41A-H) is the most posterior bone of the infraorbital series in most spe- 

 cies of Phoxinus, except P. brachyurus (see below). Infraorbital 4 meets infraorbital 3 ven- 

 trally and has no direct connection with other bones dorsally in most species. It is crescent 

 in shape and varies in the relative size to infraorbital 2 among the Phoxinus species. In 

 P. eos and erythro gaster, infraorbital 4 is slightly shorter than infraorbital 2. In P. cum- 

 berlandensis, issykkulensis, and tennesseensis, it is about the same size as infraorbital 2 

 (TS 59[0]; Fig.41B). The bone is expanded and much wider than infraorbital 2 in the re- 

 maining species of Phoxinus (TS 59[1]; Fig.41E). In P. phoxinus the bone bears a notch 

 at the dorsal portion of its posterior edge (TS 60[1]; Fig.41E). The notch is absent in other 

 species of Phoxinus (TS 60[0]; Fig.41A). 



In the outgroups, infraorbital 4 is about same size as the infraorbital 2, and bears no notch 

 at the posterior margin. 



Positioned at the dorsal side of infraorbital 4, infraorbital 5 is a small dermal bone and is 

 present in P. brachyurus only (TS 61 [1]; Fig.41A). The bone is small and irregular-shaped 

 plate-like. It is not observed in the outgroups (TS 6 1 [0] ; Fig.41B). Infraorbital 5 articu- 

 lates with the dorsal margin of infraorbital 4 ventrally, and has no direct connection with 

 other bones on its dorsal side. 



Orbitosphenoid (Fig.42A-D). In cyprinids, the orbitosphenoid is a paired chondral 

 bone. The orbitosphenoid is sutured by the lateral ethmoid anteriorly, parasphenoid 

 ventrally, frontal dorsally, and pterosphenoid posteriorly. Gasowska (1979) stated that the 

 orbitosphenoid is a single bone in cyprinids. However, Howes (1978) showed a pair of 

 orbitosphenoids in Luciobrama macro cephalus. My study on Phoxinus demonstrated that 

 the orbitosphenoid is paired in this genus. 



In Phoxinus, each orbitosphenoid is a plate-like bone. The ventral portion of the bone is 

 very thin and sutures with the same portion of other orbitosphenoid medially to form the 

 orbital septum. The orbital septum is concave at the middle or dorsal part of its posteri- 

 or margin, the ventral part of its posterior margin is convex. 



The relative position of the ventral part of the posterior margin of the septum (the very 

 thin portion of the orbitosphenoid) to the dorsal portion of the posterior margin of the or- 

 bitosphenoids varies among the species of Phoxinus. The posterior margin of the septum 

 extends posteriorly beyond the posterior margin of the dorsal portion of the orbitosphe- 

 noids in P. neogaeus. The septum almost extends to the posterior margin of the dorsal 

 portion of the orbitosphenoids in P. eos and phoxinus (TS 62[1]); the posterior margin of 

 the septum is far away from the posterior margin of the unfused portion of the orbito- 

 sphenoid in other species of Phoxinus and in the outgroups (TS 62 [0]). 



The shape of the posterior edge of the orbital septum varies among the Phoxinus species. 

 In P. cumberlandensis and P. erythrogaster, a process is present on the ventral portion of 

 the posterior margin of the septum (TS 63[ 1]). This process is not observed in other spe- 

 cies of Phoxinus and in the outgroups (TS 63 [0]). 



Pterospenoid (Fig.42A-D, 43A-B). In cyprinids, the pterosphenoid is a paired bone su- 

 tured with the orbitosphenoid anteriorly, frontal anterodorsally, sphenoid posterodorsally, 

 prootic posteriorly, and parasphenoid ventrally. In Phoxinus, the posterodorsal edge of the 



