67 



xinus and in the outgroups, the duct connects to the constriction of the gas bladder (TS 

 33[0]; Fig.34C). 



Peritoneum 



The peritoneum is an epithelial membrane lining the interior of the abdominal cavity which 

 contains the intestine and other organs. The peritoneum in Phoxinus varies in color. 'In P. 

 phoxinus, issykkulensis, and brachyurus, the peritoneum is silver with few melanophores 

 (TS 34[0]; Fig.35A). In all other species of Phoxinus (all are North American species), 

 the peritoneum is dark with numerous melanophores (TS 34[1]). 



As a rule of thumb, at least in North American cyprinids, species with a long intestine 

 always have a black peritoneum (e.g., P. erythrogaster); and species with a short intestine 

 have a silver peritoneum, except that a few species which bear short intestine have a dark 

 peritoneum. P. neogaeus is one of the exceptions. I treat a short intestine with silver 

 peritoneum as the plesiomorphic condition. 



OSTEOLOGY 



For each bone, the general morphology and its relationships with its neighbor elements 

 are described. Then a comparison on shape and size of the bone among the species of 

 Phoxinus and the outgroups are conducted, followed by a discussion on the phylogenetic 

 significance and the polarity of the transformation series in the genus Phoxinus. 

 Following Harder (1975), I divide the skeletal system of Phoxinus into four sections, i.e., 

 neurocranium, viscerocranium, vertebral column, and appendages. 



Neurocranium 



Similar to most cyprinids (e.g., Ramaswami 1955a, b), the dorsal aspect of the neurocra- 

 nium of Phoxinus is relatively flat; the posterior portion of the neurocranium is slightly 

 higher and wider than the anterior one. The neurocranium can be divided into five regions, 

 i.e.. the ethmoidal, orbital, otic, occipital, and basicranial region. 



Ethmoidal Region 



This is the most anterior region of the neurocranium. The bones in this region are com- 

 posed of dermal (e.g., nasal bone) and endochondral (e.g., mesethmoid) elements. Bones 

 included in the region are kinethmoid, supraethmoid, mesethmoid, lateral ethmoid, and 

 preethmoid (cartilage). Among them, the kinethmoid, supraethmoid, and mesethmoid are 

 single, whereas the others are paired elements. The vomer belongs to the basicranial re- 

 gion. 



In Phoxinus, the supraethmoid, lateral ethmoid, kinethmoid, and preethmoid may be ob- 

 served in the dorsal view of the ethmoidal region. The lateral ethmoid, preethmoid. and 

 kinethmoid are visible in the ventral view. The mesethmoid can be observed dorsally only 

 after the supraethmoid is removed, or posteriorly after removing the orbital region. The 

 olfactory organ is placed in the olfactory capsule which lies on the ethmoidal region. 



