59 
LETTER XVIII. To T. PENNANT, Esa. 
DEAR SIR, 
Selborne, July 27, 1768. 
I RECEIVED your obliging and communicative letter of Jime the 
28tli, while I was on a visit at a gentleman's house, where I had 
neither books to turn to, nor leisure to sit down, to return you 
an answer to many queries, which I wanted to resolve in the 
best manner that I am able. 
A person, by my order, has searched our brooks, but could 
find no such fish as the gasterosteus punffitius: he found the 
pasterosteus aculeatus m plenty.* This morning, in a basket, I 
packed a little earthern pot full of wet moss, and in it some 
twenty-five/' — Jen- Brit' Vert- p. 295. I believe the habits of the whole genus may be very safely 
inferred from those of our common L- agilis, which are almost too well known to require descrip- 
tion. They are thus concisely summed up by Mr. Jenyns : ♦* Fond of basking in th« sunshine, and 
in warm weather is extremely active. Forms a retreat under ground, in which it resides wholly 
during winter. Is first seen in March, or early in April. Feeds principally on insects. Is ovivi- 
parous, the young broods appearing in June or July. Tail extremely brittle, but, when broken, 
gradually reproduced; the renewed part, however, according to Duges, never acquires vertebra." 
When under the full influence of sexual excitement in summer, the basal part of the tail, in the 
male, is very much swollen., appearing as if the tail had been cut ofF and then set on again. In 
this state it is the L- oedura of Sheppard, an identification first pointed out b5' Mr. Gray, and 
acceded to by Mr. Jen}'ns, and which a series of intermediate specimens now before me sufficiently 
demonstrates. In conclusion, let me hope that this desultory notice will at least tend to call the 
attention of some readers towards the investigation of these neglected animals. 
Of the third order of reptiles, ophidia, but three British species appear to exist ; the brittling, 
or *' slow-worm" {anguis fragUis) , of the family anguidae; and the ringetl snake (natrix torquatxii); 
and common viper {vipera vrilgans), of the family serpentidce- A; eryx, Lin., is probably a jnere 
variety of the first, N- dumfrisien&is most probably an immature variety of the second, and the 
"red viper" {cohiou cherseaof Linnteus) is believed to be only a variety of the common one, which 
gradually loses its red colour as it increases in size. Black individuals of the common viper gome- 
times occur, but these do not constitute a distinct species. — Ed. 
* There is considerable difference of opinion among the first naturalists as to the namber ftf 
species of these minute fishes, Mr. Yarrall admitting as many as six different fresh-water kinds 
t* be found in Britain, while the Rev. L. Jenyns reduces the number to thre<*, and indeed htsi- 
tates about admitting more than two, from a consid'jration of the very great tendency of ^gas- 
terosteus acideatus to vary, and this not only in the nuinljer of bony plates along the sides, but in 
general contour and relative proportions, size and shape of the Jifferent erectiblc spines, magni- 
tude of the eyes, &c. &c., some curious and surprisinj,' instances of vihi-;h are mentioned in his 
work on the British members of the class vertebrata- i am myself disposed to concur in the latter 
opinion, having repeatedly noticed the most remarkable and striking diversities between speci- 
mens from different localities, which agree in the number of lateral osseous plates, and other 
assumed specific characters. The curious reader is however referred to Mr. Jenyns' Manunlyio 
Mr. Yarrell's admirable publication on British fishes, and above all to the ponds and brooks ia 
his neighbourhood, personal research being by far the most satisfactory means of solving diffi- 
culties and disagreements of this kind. I append descriptions which may probably asBist the 
enquirer. 
