Eeneu's — E. Koken on Fish- Otoliths. 275 



III. — Ueber Fisch-Otolithen, insbesondeke uebek diejenigen 

 DER norddeutschen Oligocan Ablagerungen. Von Herrn 

 Ernst Koken in Berlin. Aus der Zeitschrift der Deutschen 

 geologischen Gesellscliaft, 1884:, pp. 500 — 565, Tafel ix. — xii. 



On the Otoliths of Fishes, more Particularly on those of 



THE OliGOCENE STRATA OF NoRTH GeRMANY. By ErNST KoKEN. 



Journal of the German Geological Society, 1884. 



THROUGHOUT the Oligocene strata of North Germany, fossil 

 bony fishes are, to a great extent, represented merely hy their 

 detached minute otoliths or ear-bones, and the author in this paper 

 has endeavoured to ascertain the groups of fishes to which these 

 bodies belong. As the otoliths of existing fishes have not been 

 described by zoologists with suificient detailed precision to be of 

 service for comparison with the fossil forms, the author has studied 

 those of diiferent living species belonging to 60 genera of fishes, 

 and he finds that their characters are more constant in different 

 groups, and therefore more reliable for purposes of classification, 

 than many of the other skeletal structures which are generally 

 employed for this purpose. 



The otoliths are laterally compressed, elongate, to nearly circular 

 bodies, curved, so that the outer side is mostly concave, whilst the 

 inner is convex. On the convex inner side, extending from the 

 anterior to near the posterior margin, is a long impression or sulcus, 

 and on the various modifications of this sulcus the more distinctive 

 charactei'S of the otoliths rest. The concave outer side of the otoliths 

 is marked by radiating folds or tubercles, or by a combination of 

 both. The otoliths are formed by successive concentric layers of 

 minute crystalline rods of calcite, and these minute particles have a 

 definite angular disposition in relation to radial lines extending from 

 the centres of the otoliths. On this minute interior structure the 

 surface characters depend, and it is constant for each species. 



Genuine otoliths are only present in the auditory organs of Tele- 

 osteans and Ganoids ; in Sharks, Rays, Chimeroids and Cyclostomi, 

 there are only loose irregular aggregations of small crystalline par- 

 ticles of calcite. From the otoliths present in the Oligocene strata 

 of North Germany, the author has determined 21 different species of 

 fishes, belonging to 8 families, viz., the Gadidce, Percidce, Apogovida, 

 TracliinidcB, Scicenidce, SparidcB, TriglidcB, and Pleuronectidce. Of these, 

 the GadidcB or Cod family is distinctly predominant, and it is repre- 

 sented by 7 species, of which 2 belong to Gadus itself. Professor 

 Prestwicb also records that the otoliths from the Norfolk and Suffolk 

 Crag belong to Gadus and allied genera.^ 



Otoliths very seldom occur in their natural position in the entire 

 fossil skeletons of fishes, though a few cases are known from beds 

 in which fossil fishes are very abundant and well preserved. On the 

 other hand, they are by no means uncommon in beds in which no 

 other remains of fishes are met with. This fact may perhaps be 

 explained from the facility with which they would fall out from the 



^ Quart. Journ. Geol. Soc. yoI. xxvii. p. 132, 1871. 



