ESPECIALLY MYCTOPHOIDS 51 
Genus DERCETIS Agassiz, 1834 
1863 Leptotvachelus von der Marck: 59. 
1940 Benthesikyme White and Moy-Thomas : 102. 
DiaGnosis (emended). Dercetidae in which the head is more or less extended, 
with premaxilla produced slightly in advance of the mesethmoid. Body region 
always extended. Mandible extends to the anterior tip of the snout. Teeth 
clustered and in the form of slender hollow cones, present on premaxillae, maxillae, 
dentaries, palatines and ectopterygoids. Paired fins prominent with pectorals larger 
than the pelvics. Dorsal fin more or less extended, in the mid-region of the back. 
Anal fin short and remote. A single pair of transverse processes per centrum. 
Anterior precaudal centra at least twice as long as deep. Dermal scutes in a paired 
series along dorsal and ventral borders and in a single series along lateral line ; a 
few large lath-shaped intermediate scutes in larger species, but squamation never 
complete. 
TYPE SPECIES. Dercetis scutatus Agassiz. 
REMARKS. The genus was erected by Agassiz (1834 : 390, and Feuill.; 20) to 
include the type species Dercetis scutatus from the Upper Senonian deposits of 
Baumberg, Westphalia. Later von der Marck (1863) erected another genus within 
the family Dercetidae to include the new species Leptotrachelus armatus (59, pl. 10, 
fig. 3). In 1873, von der Marck added a further species, Leptotrachelus sagittatus 
(63, pl. 2, fig. 1). Both of these species were erected on imperfect material from the 
Upper Senonian (Campanian) of Sendenhorst, Westphalia, and his type material is 
located in the Paldontologisches Institut der Westfalische Wilhelms-Universitat, 
Minster. Since 1873 several more species of both genera, Dercetis and Lepto- 
trachelus, have been erected, the material coming from various localities such as the 
Chalk of S.E. England, the Niobrara Chalk of Kansas and from the Sahel Alma 
locality in the Lebanon. 
The holotype of Dercetis scutatus (at one time in the Bayerische Staatssammlung fiir 
Palaontologie, Munich) appears to have been either lost or destroyed. Unfor- 
tunately no other specimens of the type species could be traced. After examination 
of most of the species placed in the genus Dercetis from the English Chalk, together 
with the examination of both the Leptotrachelus species erected by von der Marck, 
and those leptotrachelids from the Lebanon, it is clear that they all belong in a single 
genus. This conclusion is in accordance with that of Siegfried (1966 : 215), who 
has examined and redescribed von der Marck’s material, and as a result moved both 
to the genus Dercetis (Dercetis armatus (Text-fig. 24) and Dercetis sagittatus). 
Several species of Leptotrachelus from Sahel Alma have been studied but all of the 
material is fragmentary and badly preserved. The descriptions are therefore 
incomplete but even so are sufficient to show that these species also belong to the 
genus Dercetis. The three species from Sahel Alma, Dercetis triqueter (Text-fig. 23), 
Dercetis gracilis (Text-fig. 25) and Dercetis rostralis (Text-fig. 26), although still 
considered to be three separate species, are arbitrarily separated. Thus considering 
all the Dercetis material available a graded series is apparent, ranging from the 
