43 



bital septum lower: (18) orbital septum connecting broadly with the dorsal aspect of the 

 parasphenoid: (20) supraorbital bone large (reversal): (25*) metapterygoid bearing a deep 

 notch at its posterior margin: (27) the most anterior supraneural bone large. One species. 

 C. plumbeus (Agassiz. 1850). is included in the genus (Robins et al. 1991 ). which mainly 

 occurs in the western United States and Canada (Well 1980). 



Semotilus Rafmesque. 1820a has three apomorphies: (5) the left and right portions of the 

 supratemporal canal connected (reversal): (16) anterior margin of orbital septum forming 

 an anterior process: (27) the most anterior supraneural bone large. 



Four species. Semotilus atromaculatus (MitchilL 1818). S. corporalis (Mitchili. 181 7 ). 5. 

 lumbee Snelson & Suttkus. 1978. and 5. thoreauianus Jordan. 1877 belong to Semotilus. 

 The genus occurs mainly in eastern North America (Lee &. Platania 1980. Gilbert 1980. 

 Snelson 1980. Johnston & Ramsey 1990. Robins et al. 1991). A phylogenetic hypothesis 

 of relationships among the four species of the genus was proposed by Johnston & Ram- 

 sey (1990). 



Discussion 



The relationships between Phoxinus and other minnow genera are an interesting and chal- 

 lenging problem that has attracted many ichthyologists" attention. At least four hypothe- 

 ses have been proposed by previous authors through different approaches. My hypothesis 

 on the phylogenetic relationships of Phoxinus with other genera (Fig.l8C) differs from 

 the previous ones. A brief discussion of the previous hypotheses is presented below. 

 Hypothesis 1: In a study of life history of Clinostomus elongatus. Köster (1939) noted 

 that breeding males of Clinostomus, Margariscus. and Couesius had similar breast tuber- 

 culation. Koster (1939) therefore proposed a close relationship between Phoxinus and the 

 group formed by Margariscus. Clinostomus. and Couesius. Köster (1939) correctly reco- 

 gnized the close relationships of Margariscus and Couesius. However, the breast tuber- 

 culation differs between Phoxinus and the group including Margariscus and Couesius. as 

 discussed above. The breast tuberculation of Clinostomus elongatus is similar to that in 

 Margariscus and Couesius. but this character might be homoplastic because Margariscus 

 and Couesius are said to belong to the Chub clade. whereas Clinostomus belongs to the 

 Shiner clade (Coburn & Cavender 1992). 



Hypothesis 2: Like Koster 1 1939). Howes ( 1985. 1991 ) proposed a sistergroup relations- 

 hip between Phoxinus and Couesius (forming the phoxinins of Howes) supported by the 

 breast tuberculation. Two problems are present in this hypothesis. First. Howes did not 

 recognize the observation that the breast tuberculation is also present in Margariscus. Se- 

 motilus. and Clinostomus (and he also seemed to be not aware of Koster's publication). 

 Therefore, if the "breast tuberculation"' of all genera bearing the tuberculation could be 

 evaluated as homologous structures, more genera should be included in the phoxinins of 

 Howes. Secondly, the breast tuberculation patterns of Phoxinus and Couesius are not si- 

 milar one another (Chen & Arratia 1996). As discussed above, the breast tuberculation in 

 the two genera should be evaluated as two transformation series. Therefore, the breast tu- 

 berculation does not support the sister group relationships of these two genera. 



