180 ON TRIGLA PCECILOPTERA AND TRIGLA HIRUNDO. [Feb. 18, 



I have found, however, 10 caecal appendages in T. poeciloptera, 

 whereas in Cuv. and Val. T. hirundo is said only to possess 8. But 

 on reexamining this point, I find my examples of the latter fish also 

 have 1 ; consequently this feature may be subject to individual varia- 

 tions. Until I possess more examples I slialj be unable to ascertain the 

 number of vertebra?, or make detailed investigations as to the sexes. 



The air-vessel in the various species of this genus afford excellent 

 characters for discrimination ; so I have been careful in ascertaining 

 what its appearance is like in T, poeciloptera. At bk inches it is oval, 

 with two short projections anteriorly, one on either side, and behind 

 them laterally is a short tube, which does not extend backwards 

 along the outer side of the air-vessel more than one fourth of its 

 length. In another example of the same dimensions these lateral pro- 

 longations extended backwards about one half of the length of the air- 

 vessel on either side ; and in my largest example (9"8 inches in length) 

 they nearly reach its posterior extremity. 



Among the British species of Trigla destitute of elongated fin-rays 

 (such as T. obsc\ira\Jmn.), three have the lateral line armed or rough- 

 ened, viz. T. lineata, Ray, T. gurnardus, Linn., T. cuculus, Bloch ; 

 but as the lateral line is smooth in T. pceciloptera, any immediate 

 relaiionship between these forms is excluded. Those with the lateral 

 line smooth are T.pini, Bloch, and T. lyra, Linn., in neither of which, 

 according to Cuv. & Val., has the air-vessel any lateral process ; but 

 in the third, T. hirundo, Bloch, we find a lateral process on either 

 side extending backwards as is seen in T. pcecilojjtera. 



It is evident that in the " Little Gurnard " these processes aug- 

 ment in extent with the age of the fish ; but I have not seen them 

 reaching round the posterior extremity of the air-vessel, as I have 

 found them doing in large examples of T. hirundo ; I have, however, 

 found them two thirds of the length of the air-vessel in examples' 

 about 6 inches in length. I have not seen any very young speci- 

 mens of T. hirundo ; neither do I know of their having been recorded, 

 unless in the form of T. poeciloptera. 



In the very young, these fishes appear to be unsociable, keeping near 

 the bottom of the water and spreading out their pectoral fins so that 

 they appear hke beautiful blue butterflies with white and light-blue 

 spots on either wing. As they increase in size the dimensions of 

 the spotted portion of the fin decrease ; and in some cases it seems to 

 disappear. In 2'. hirundo, on the contrary, the inner side of the pec- 

 toral fin is blue, with transverse black bands in its whole extent. 

 Curiously, one of the examples on the table, upwards of 9 inches in 

 length, has one pectoral fin coloured as in T. hi?-undo, v/hereas the other 

 shows unmistakable evidence of the remains of the immature spot. 

 As a rule, fins with the large spot are only banded on their outer two 

 thirds ; while fins destitute of spots are banded in their whole extent. 



P.S. Since the foregoing was written 1 have seen, in the collection 

 of the British Museum, several examples of the young of T. hirundo 

 having the vivid colours of T. pceciloptera, seven being from Wey- 

 mouth ; while the following specimens still have traces, to a greater 

 ' All these varions sizes are present on the table. _ 



