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Show 180 ON TRIGLA PCECILOPTERA AND TRIGLA HIRUNDO. [Feb. IS, I have found, however, 10 caecal appendages in T. pceciloptera, whereas in Cuv. and Val. T. hirundo is said only to possess 8. But on reexamining this point, I find m y examples of the latter fish also have 10 ; consequently this feature may be subject to individual variations. Until I possess more examples I shall 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. pceciloptera. At 5| inches it is ovaj, 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 prolongations extended backwards about one half of the length of the air-vessel on either side ; and in m y 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. obscura Linn.), three have the lateral line armed or roughened, viz. T. lineata, Ray, T. gurnardus, Linn., T. cuculus, Bloch ; but as the lateral line is smooth in T. pceciloptera, any immediate relationship 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. pceciloptera. It is evident that in the " Little Gurnard " these processes augment in extent with the age of tbe 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 examples1 about 6 inches in length. I have not seen any very young specimens of T. hirundo ; neither do I know of their having been recorded, unless in the form of T. pceciloptera. 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 like 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 T. hirundo, on the contrary, the inner side of the pectoral 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. hirundo, whereas the other shows unmistakable evidence of the remains of the immature spot. As a rule, fins with the large spot are only handed on their outer two thirds ; while fins destitute of spots are banded in their whole extent. P.S. Since the foregoing was written I 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 Weymouth ; while the following specimens still have traces, to a greater 1 All these varions sizes are present on the table. |