S.L. 

 ISO- 



IS 20 2S 



BODY DEPTH AS 



CAUDAL PEDUNCLE DEPTH AS 



Figure 46. — Charts show two proportional 



measurements as percent of standard 



length that differentiate Acanthopleurus 



aerratus and A. collettei. 



(2) 1.5-3.9% SL; distance between tip of snout and spiny 

 dorsal fin origin (1) 24.1'^c SL; length of pelvis posterior 

 to region of axil of pelvic spine (3) 14.7-15.6 (15.1)% SL. 



Comparable proportions of A. serratus are as follows: 

 greatest depth (9) 16.0-21.8 (17.3)% SL; least caudal 

 peduncle depth (5) 3.8-4.7(4.4)% SL; length of pelvic 

 spine (7) 19.7-28.2 (22.9)^p SL; length of first dorsal 

 spine (9) 19.7-29.5 (23.7)% SL; length of second dorsal 

 spine (1) 8.6% SL (third and subsequent dorsal fin 

 spines not measurable in any of the specimens exam- 

 ined); distance between tip of snout and spiny dorsal fin 

 origin (1) 31.1' < SL; length of pelvis posterior to region 

 nf axil of pelvic spine (2) 17.6-17.8'^r SL. 



In reviewing the Oligocene fishes of the black schist of 

 Canton Glarus, Wettstein (1886) believed that the dif- 

 ferences in depth of the specimens of Acanthopleurus 

 were due to distortion. However, many of the specimens 

 of both A. serratus and A. collettei seem to be in ex- 

 cellent proportion, and the impressions of the scales and 

 of their orientation and spacing do not seem to me to be 

 distorted, as one would expect them to be if the slender 

 specimens were simply artificially stretched out versions 



of the deep-bodied specimens. Moreover, in the few 

 specimens of both species in which the sculpturing of the 

 scales can be at least partially deciphered, it appears 

 that A. collettei had a series of vertical emarginate 

 ridges, approximately like those of the Recent Pseudo- 

 triacanthus, while A. serratus had more of a cruciform 

 emarginate ridge, approximately like that of the other 

 three Recent genera of triacanthids. It seems clear that 

 at least two species of Acanthopleurus were present in 

 the Oligocene seas of Europe. 



Both species of Acanthopleurus have the first dorsal 

 and pelvic spines as well developed as in Recent species, 

 and with a similarly roughened surface. As in most of the 

 Recent species, the second dorsal spine is less than half 

 (about one-third) the length of the first spine, with the 

 third and fourth spines progressively smaller. None of 

 the impressions of Acanthopleurus show a fifth or sixth 

 spine, but such could easily have been present but not 

 indicated in the impressions at such small size. 

 Epipleurals appear to have been as well developed on the 

 abdominal and more anterior of the caudal vertebrae as 

 they are in the Recent species. The dentition is not clear 

 in any of the specimens of Acanthopleurus, but some 

 specimens clearly show the presence of 12 caudal rays in 

 a deeply forked fin. There appear to have been 12 caudal 

 vertebrae in the few specimens that show this region rela- 

 tively well, while the abdominal vertebrae cannot be 



