TlUtlCE-UKAliDKIJ UOCKLING. 



551 



wliotlier he really distingiiislied between it and Linn.kus's Gailus iiiedi- 

 ferranetis, and he was evidently doubtful himself on this point. Still, 

 wlieii he says that it is more eoniinim in (lie Atlantic on the eoasl of 

 (.'(■rnwall than in Un; Jlediterranean and the Adriatic, he undoubtedly 

 refers [irincipally to our species. Bi.ocil's description and li<;nre (Aiist. 

 Fi.wlie, Th. II, p. 100; pi. CLXV) are no less obscure; but the 

 names of I'hree bearded cod in Pknnant and Gadus tn'rirrnlns in 

 Donovan (1808) defend Nii.sson's Molella ti-idrrata. 



Risso {I'Air. Mer.) distinguished between lliroe Mediterranean 

 species of this genus (0/(06' mustella, On. mactdntus, and On. /».w«.s), 

 but liased tin's distinction on the chromatic characters alone. Costa 

 (Fii. lieijn. X(ij)., Fesci, Malavott., tSottol/r., \t\>. 17 and 39, tav. 

 XXXVIII, bis) recognised only two, one {Motella communi.t) corre- 

 sponding to Risso's Onos fitscus, the other to the Onos mnculatns of 

 the latter and coinciding with LiNN/>;us's Gadus meditervaneus (6'i/st. 

 Nat., X, tom. 1, p. 25.5; J///s. Ad. Frid., toni. II:di prodr., p. 00). 

 The latter species was described by Canesthini (Arch. Zool., Anat., 

 Fisiol., vol. II, p. :i69, tav. XV— XVI, fig. 2) from the Gulf of Genoa, 

 under the erroneous name of Motella commnins. Collett, Lt)TKEN, 

 and LiLUEBORG give true form-characters to distinguish between two 

 Mediterranean species, the one identical with the Three-Bearded Rock- 

 ling, the other with LiNN.liUs's Gadus meditevfuneus. Moreau, like 

 Risso, hut on better grounds, distinguislied between three Mediterranean 

 species: Motella tricirrata (Risso's Onos mustelhi), Motella maculata 

 {Onos maculatus, Risso), and Motella fnsca (Onos fuscns, Kisso). On 

 the chronuitic character we can hardly ])ass any opinion, for the only 

 specimens we have been enabled to examine were preserved in spirits". 

 The form-characters, on the other hand, show an extremely close con- 

 nexion between the three species. In most characteristics Onos fuscus 

 is an intermediate form between Onos mediterraneus and Onos tri- 

 cifratus, thus impairing the validity and usefulness of these charac- 

 teristics. This is the case for example with the difference pointed 

 out by Moreau in the length of the upper jaw from the tip of the 

 snout to the hind extremity of the maxillary bones. In our speci- 

 mens of Onos mediterrantus this length is exactly '/o, in the speci- 

 mens of Onos fuscus .51','., — 52 "o, and in those of Onos tricirratus 

 5.S — nearly 58 K, of the length of the head. Again, as far as we 

 can judge from our materials for examination, the breadth of the inter- 

 orbital space in Onos mediterraneus is less than 30 %, in On. fusctis 

 more than 30 bnt less than 33 %, and in 0)i. tricirratus more than 

 35 °i, of the posforbital length of the head. The length of the upper 



jaw in On. mediterraneus is less than 30 %, in On. fuscus more than 

 30 but less than 34 %, and in On. tricirratus more than 34 %, of 

 tlic distance between the second dorsal tin and the tip of the snout. 

 The lengtli of the lower jaw in On. mediterraneus is less than 33 %, 

 in 0)1. fuscus more than 33 hut less than 3G %, and in On. tricir- 

 ratus nior(^ tlian 38 %, of tlie distance just mentioned. The length 

 of the base of the first dorsal tin in On. mediterraneus is more than 

 74 %, in On. fuscus less than 70 but more than l36 %, and in On. 

 tricirratus less than 113 %, of the distance between the first dorsal 

 fin and the tip of the snout. Onos fuscus occupies this intermediate 

 position in spite of the fact that, according to Moreau, it never at- 

 tains tlie same size as the two other species, a circumstance which 

 is especially worthy of remembrance in the case of the specimens we 

 have examined, among which the specimens of Onos fuscus are almost 

 exactly equal in size to tlie youngest specimens (jf Onos tricirratus. 

 In the characters winch sliow distinct changes of growth connnon to 

 all tliree species (rising or falling percentages as expressions of the 

 relative proportions of form), this intermediate position shonhl thus 

 be explained as the expression of a more advanced development at a 

 smaller size in the case of On. fuscus. Hut in some respects the 

 iidermediate position does not hold good, and On. fuscus ranks beside 

 the younger specimens of On. tricirratus, or takes a lower place in 

 the scale of development than they. This is the case for example 

 in tlie relation between the breadth of the interorbital space and the 

 least depth of the tail, a relation which, though it does not afford 

 any constant characteristic difference, still shows di.stinct changes of 

 growth. In other relations again, as for example in the least depth 

 of the tail expressed in proportion to the distance between the second 

 dorsal fin and the tip of the snout, where we have a constant di- 

 stinction between Ou. tricirratus and tlie other two species, On. fuscus 

 stands nearer On. mediterraneus. Finally, in other relations, in which 

 the direction of development is different in On. mediterraneus and 

 On. tricirratus, On. fuscus, like the early stages of these two spe- 

 cies, points still more distinctly to the original starting-point common 

 to the development of the other two species. As an example of 

 this we may take the relation between the posforbital length of the 

 head and the distance between the second dorsal fin and the tip of 

 the snout. This length, expressed in percent of the said distance, 

 relatively decreases with increasing age in On. mediterraneus, but 

 increases in On. t?'icirratus, according to the following results of our 

 measurements: 



S J) e r i III (■ n 





^ , , ,,, ,. ., Least depth of tlie tail 

 Least lireiidtli of tlie . ., ,',, ,. . 

 . , , ., , . I in ?< of the distance 



interorbital space in , . ., , 



„.„.,, i. 1 ^i , lietween the second 

 % of the least depth , , ^ , ., 



„.,..., ^ dorsal tin and the tip 

 of the tail. ,. ,, , ' 



of the snout. 





11 



Pnstorbital length of 

 the head in % of the 

 distance between the 

 second dorsal fin and 

 the tip of the snout. 





Island-belt of (iotlicnbiiri;, through .\. Stlxhekg _ 



Kergen, through the Museum of Upsala University, cf -- 



Nice, through T. Thokei.i., s|u'ciiiicn in possession ut the ^luseuiii of Upsala University.. 



Locality unknown, from the 1*aykl'LL Collection in the Itoyal Museum 



Algiers, the property of the .Museum of Upsali University 



Mediterranean, LiNN.-EUs's type-specimen, I'roui l)rottiiini:hnlni Museum - 



Naples, through the Zoological .Station, cf - 



Nice, through T. Thokeli 



Naples, through the Zonlogical Station, 9 



Xiee, through T. Thorell 



23.9 

 22.7 

 19.1 



19.1 



20.0 



34.9 

 36.3 

 37.7 



" It is a known fact, however, that young Three-bearded Rocklings at the termination of the foHi7(/a-period are of a 

 lirowu colour, darker or lighter, and do not show any traces of spots until fliey have attained a more advanced age. 



42.1 

 41.8 

 41.5 



40.2 



41.4 



39.4 



39.4 



plain reddish 



