10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I42 



(16 branched rays). Preliminary analysis showed that the difference 

 in ray count occurs in the upper caudal lobe (9 branched rays in 

 cyprinids, 8 in suckers). To pinpoint the position of the lost ray an 

 effort was made to relate the rays to the hypural on which they origi- 

 nate. Here the complication was promptly encountered that in both 

 cyprinids and suckers the number of hypurals extending to the upper 

 caudal lobe varies between 3 and 4. In the catostomids examined, 

 almost all had 4 upper hypurals, though the uppermost (fig. iD) 

 is sometimes quite small ; the only exception was in Erimyzon 

 sucetta, where, in three specimens examined, the uppermost hypural 

 was missing completely. In the Cyprinidae, on the other hand, the 

 majority of forms examined had only 3 upper hypurals, but Carassitis 

 auratus (two specimens), Semotilus corporalis (two specimens), and 

 Campostoma anomalum (one specimen) had 4. Though the number 

 of 3 or 4 seemed to be constant within species in the available material, 

 no relationship between hypural number and the systematic position 

 of the species could be discerned. When an attempt was made to 

 relate certain caudal ray bases with specific hypurals, it was discovered 

 that the number of ray bases articulating with any one hypural varied 

 by plus or minus 2 (compare Makushok, 1958, p. 11), even when 

 members of the same family with the same number of hypurals were 

 compared. Furthermore, it was found that some of the ray bases 

 extended over parts of two hypurals. From all this it was concluded 

 that there is no close correlation between the caudal ray bases and the 

 hypurals in cyprinoid fishes. It was also concluded that for systematic 

 purposes in cyprinoids a difference of one hypural has less significance 

 than the difference of one branched ray. However, the mystery of 

 the disappearing ray in the upper caudal lobe of catostomids remains 

 unsolved. 



Order Scopeliformes. — Among the iniomous fishes caudal skeletons 

 of the genera Aulopus, Synodus, Chlorophthahnus, Solivomer, Lam- 

 panyctiis, Omosudis, Lestidium, and Alepisaurus have been examined. 



Aulopus differs immediately from all the others in the retention of 

 bony fulcral scales in front of the accessory caudal rays above and 

 below. As to the caudal skeleton itself, the basic features of caudal 

 structure shown for Chlorophthahnus (fig. 2B) are found throughout 

 these genera. The terminal vertebra and postterminal centrum i have 

 fused into an elongate structure ; a separate postterminal centrum 2 is 

 frequently visible in lateral view ; the anterior uroneurals have a high 

 median crest (probably a neural arch structure) but are never fused 

 with the centra below (except perhaps in Lampanyctus) . 



