711 
No. 145.] 
History, under the name of Eriosoma Pyri. All those Plant lice 
which were formerly included in Dr. Leach’s genus Eriosoma , 
which have all the veins of the wings simple, and those in the 
disk of the hind pair two in number, now form the genus Pem¬ 
phigus of Hartig (Germar’s Zeitsch. vol. iii. p. 366), to which 
genus it is therefore necessary to refer this insect.* Several of 
the other species of this genus, as well as the present one, are 
known to infest the roots of plants. I entertain scarcely a doubt 
that this is the same species which Mr. Walker soon afterwards 
described, from specimens obtained in Nova Scotia, under the 
name of Pemphigu Americanus; though the length which he as¬ 
signs to it (four lines) is rather greater than any individuals I 
have met with. 
t 
To our nurserymen it obviously belongs, to fully elucidate the 
history of this species, and the disease which it occasions, as they 
enjoy opportunities tor observing it such as belong to no other 
profession. The knots, or excrescences, occur both upon the large 
• Mr. Westwood, in his Arcana Entomologia, vol. ii. p. 63, observes that the name Bryso- 
crypta (Byrsocrypta) of Haliday must be retained for Ilartig’s genus Pemphigus. And on 
the next page we are told: “The generic name of Eriosoma (Leach) must take place of 
that of Pemphigus , and bo restricted to such species as differ from Aphis bursarius.” There 
is a contradiction here, which I can only account for by supposing the distinguished author, 
who is so accurate a noinenclator, has inadvertently placed the name Pemphigus in the lat¬ 
ter quotation, where he intended to insert Schizoneura. Tho first division of the old Lin- 
na?an genus Aphis appears to have been made in 1819, when Sarnouelle (in his Entomologist’s 
Companion, p. 232) published the genus Eriosoma from Dr. Leach's MSS., with the “ E. 
Mali, the Aphis lanigera of authors,” or the well-known Apple tree blight, as its type. 
Samouelle's little work, truly a “ Useful Companion” in its day, probably was not circulated 
upon the Continent, and entomologists there seem to have been uninformed of its oontents. 
Several synonyms, in consequence, have unfortunately been introduced into the science. Five 
years afterwards, Blot (in the Memoirs of tho Linnman Society of Calvados, vol. i. p. 114) 
named tho same insect Myzoxylus Mali , which name has been extensively circulated by 
French writers. Still more recently, Hartig (in Germ.vr's Zeitschrift, vol. iii. p. 367) has 
proposed the name Schizoneura for this same genus; whilst Macquart has bestowed the name 
Eriosoma upon a genus of flies, in the Order Dip*era. Mr. Westwood is clearly right in re¬ 
taining Dr. Leach's name for the genus*having Aphis lanigera os its type. 
With regard to tho statement first made above, I would observe, Mr. Haliday first proposed 
the genus Byrsocrypta, if I mistake not, in the Annals of Nat. Hist, for the year 1839, page 
189, placing under this genus the Aphis Ulmi of Geolfroy, and a new species which he names 
pallida. We hence regard the Ulmi and not the bursarius as the typo of Mr. Haliday’s 
genus. Consequently the namo Byrsocrypta must be retained for the genus which has Ulmi 
for its typo, namoly, the Tetraneura of Hartig; whilst his genus Pemphigus, with bursarius 
as its type, is entitled to stand. I therefore givo our American species under this namo. 
