Williston.] Cretaceous Fishes. 381 



form of a double trapezium, with the V posterior, the middle 

 raised into a well-marked carina, which runs from the head to 

 the tail. Apparently there are five rows of these scutes on the 

 body. At the front the topmost row is near the middle line, 

 the lateral row has its lower edge over the line of the vertebrae, 

 while the lowest row has the carina just below the pectoral fin. 

 The scutes have a finely roughened appearance, due to minute 

 rounded and shallow pits. There are no indications of small 

 scutes on the body intermediate between the larger ones. 



Length of fish, as preserved 2-40 mm. 



Estimated length 250 " 



Length of vertebral column 175 " 



( i reatest width, just back of pectoral fin 27 " 



Length of caudal fin, upper lobe 22 " 



Length of pectoral fin 7 " 



Length of ventral fin 9 " 



The specimen lies on the shell of a large Inoceramus, explain- 

 ing its excellent preservation. Close by are the remains, as 

 seen in the illustration, of several examples of a small fish of 

 unknown affinities, hitherto undescribed. The horizon is the 

 Niobrara Cretaceous of the Smoky Hill river. The specimen 

 was collected by Mr. H. T. Martin in 1895. 



"The family Hoplopleuridte was established by Pictet for 

 fishes which were devoid of scales properly so-called, but which 

 are protected on the back and sides by rows of scutes. The 

 head is long and the jaws are provided with pointed teeth of 

 unequal size. The bones of the head are frequently sculptured 

 or granulose. The genera associated in this family by M. Pic- 

 tet are: Dercet is Agassiz, Saurorhamphus Heckel, Leptotrachelus 

 Von der Marck, Plinthophorus Guenther. Euryophilus Pictet, Pe- 

 largorhynchus Von der Marck. The fishes included in the genus 

 D< rcetis were considered by Agassiz to resemble the sturgeons in 

 the arrangement of the dermal scutes, and were grouped among 

 the ganoids. Heckel held the same opinion with respect to the 

 position of Saurorhamphus, and Von der Marck also places the 

 genera Pelargorhynchus and Leptotrachelus amongst the ganoids, 

 but regards Ischyrocephalus as a teleostean. A careful review 

 of the whole of the genera, assisted by additional specimens o 



