COTTOIDS. 



163 



(^puiridcrniirlifl/i/s mid GifninoniHtlnis iirc in sevcrnl re- 

 spects simil.-ir to those which genei'nlly exist between 

 tlie true Cotti and the fresh-water members of the 

 famih . In the former genus, for example, tlie mouth 

 is laimn' and the anal tin shorter: the length of the 



and thi' fresh-watei' Cotti, we find, too, in the genus 

 Centridermichthys, even in the two species of which we 

 have now to treat, a distinct approach towards Gi/mno- 

 canfJiKs. 



In the basin of the Atlantic Centridermichthys, as 



ma\ill;irv bones is never less than W % of that of the \ well as tlie preceding genus, contains only forms which 



body, and the lengtli of the anal tin seldom exceeds j belong to the extreme north, but in the Pacific at 



25 % of the length of the body, i. e. tlie length of the i least one species is found as far south as the Philip- 



maxillarv bones is never less than 44 % of that of ' pine Islands. The number of species is not great: only 



the base of the anal tin. However, just as we can I 8 are known, most of them from the west coast of 



scarcely draw a generic distiiu'tiou l)etween the true ! Noi'th Americ-a. 



CENTRIDERMICHTHYS UxXCINATUS. 



Fig. 49. 



Skin naJi-ed, trithoxt scales or the corresponding spinous formatiotis, but sometimes irith soft irarts on the top) of 

 the head, <is irell as on the Itark (d)ove the lateral line. The tiro middle spines of the preoperculum almost tvanting 

 or only slightly d er eloped : tlie upper spine bent. pointi}ig backirards in an npirard direction, and often with a 

 lateral spi)ie at the base: tlie loiver pointing forwards in a downward directioti. Only tiro slightty-developed spines 

 on the top of the head, corresponding to the posterior {occipitcd) spines in the other Colloids. On the hind part 

 of the maxillary bones a smcdl, conical, dermcd flap. A similar flap sometimes 0)i the hind part of the skin u'hicli 

 covers the upper part of tlie eyes. Head fairly low and fat, its length from 28 to 30 % of tliat of the body. 

 Length of the maxillary bones less than 12 % of that of the body, or from 57 to GO % of that of the base of 

 the anal fin. Length of the lower jaw less titan 15 % of that cf the body. Length of the base of the second 

 dorsal tin less than 27 % of that of the body. Length of the base of the anal fin at least 80 % of that of the 

 base of the seco)id dorsal. Least breadth of the intcrorbital sp)ace less than half {from SO to 40 % of) the least 

 depth of the tail. Urogenital papilla of the male small". Eggs fen- and large''. Coloration light oil-broum on the 

 back, yelloirish irhife on the belly: 3 dark-brown transverse bands on the dorsal side — in yotmg specimens a similar 

 band on the head above the orbital region — but these transverse bands are generally broken up into an irregular 

 mass of spots. Dorsal, pectoral and caudal fins with similar transverse ba)ids : anal and ventral fins of the same 



colour as the belly, but sometimes with transverse bands or spots. 



Fis:. 49. Ceiitridermiclithi/s iincinatus, taken at a depth of from 5 to 10 fathoms, on a rocky, algous bottom, in Actinia Bay on the north 

 coast of Taimyr Sound, in Aug., 187S. Temperature of the water at the bottom ■29'9' Fahr.; at the surface 3.3'6' Fahr. Natural size. 



Ol)S. The proportions given here, founded upon measurements 

 of two males and two females, are intended to show, in comparison 

 with the preceding genus and the following species, firstly, that the 

 specific difference in Centrideniiclithi/s follows tlie same rules as in 



Gi/mnocanthtis as described above, and secondly, that the characters 

 of Ucntr. Iincinatus, compared with those of U. hamatus, generally 

 indicate a successive approach to Gymnocanthtis. 



" It is, however, uncertain whether males ready to spawn have been examined. 



'' In two females respectively 87 and 92 mm. in length, from the Arctic Ocean off Ljakoff's Island (Siberia), taken in September, 

 1878, the eggs were about 2','3 mm. in diameter. Collett (1. c.) estimated tlie number of the eggs in females taken by the Norwegian 

 Arctic Expedition at about 60. 



