30 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



The preoperculum is strongly serrated, its posterior border being produced 

 into very prominent spines. The margiiud teeth are conical and arranged in 

 single series, no pharyngeal teeth being observed. The vertebrae are about 

 25 in number, of which 14 are caudal. The dorsal fin is much extended, with 

 about 26 rays, and of these 11 are spinous. The caudal is composed of 17 

 principal rays, there being one more in the upper than in the lower lobe, and 

 these are preceded both above and below by four or five spinelets. The anal 

 appears to be formed of about eight rays in addition to the spines, but their 

 number cannot be accurately counted. There are at least eight branchiostegal 

 rays. Evidence of the former extension of the scales over the opercular bones 

 and cheeks is not apparent in the present condition of the specimen, nor in fact 

 is it ordinarily to be expected amongst fossils. The scales are thin, ctenoidal, 

 and very strongly pectinated. 



Crenilabrus was separated by Cuvier from Labrus as a distinct genus on 

 account of its having a serrated preoperculum, but it has been shown by D. S. 

 Jordan in his Review of Labroid Fishes ^ that the form is identical with the 

 earlier described Symphodus of Rafinesque. 



CHAETODOXTIDAE. 

 PYGAEUS Agassiz. 



To this imperfectly known extinct genus have been referred half a dozen 

 species from the Bolca Eocene, and two from the Lower Miocene of Chiavon, 

 Yicentin. The type species is P. bolcanus (Voltu), renamed P. gigas by Agassiz. 

 This is a large form, attaining a total length of about 35 cm., the remaining 

 species being very much smaller, and included by Agassiz only provisionally 

 in the same genus with the type. It appeared to Agassiz that the smaller 

 forms constituted a group by themselves, typified by P. coleanus, but passing 

 over into the group of larger forms through the intermediate P. ohlongus. Con- 

 cerning the advisability of subdividing the genus, Agassiz remarks as follows: 

 "II faudra done probablement demembrer un jour ces especes et en faire 

 autant des genres qu'on y reconnaitra de types differents, en les etudiant d'une 

 manifere plus complete; ce qui sera d'autant plus difficile que les Pygees sent 

 fort rares dans les collections." 



There are in addition to the small number of forms known to Agassiz two 

 other species represented by a solitary individual each, which are evidently 

 closely akin to Pygaeus bolcanus, although possessing more finely divided 

 vertical fins. These are the so-called Acanthurus gazolae Massalongo ^ and 

 A. gaudryi de Zigno,^ from the Bolca Eocene, whose true position amongst 



1 Jordan, D. S., A Review of the Labroid Fislies of America and Europe, Kept. 

 U. S. Fish Comm. for 1887, pp. 559-699, 1891. 



2 Specimen Photogr. Anim. Foss. Agr. Veron., 1859, p. 20. 



3 Atti R. Istit. Veneto, xxiii. 1887, p. 14, Fig. 2. 



