REPORT ON THE ANNELIDA. 
173 
Measurements. 
Antero-posterior diameter of globe (from cornea to centre of cephalic ganglion) = 0'25 mm. 
Transverse diameter of globe = 0’22 mm. 
From centre of ganglion to pigment on free surface of ganglion = 0T mm. 
From pigment on ganglion to anterior surface of vitreous = 0’05 mm. 
Thickness of cornea = 0'002 to 0‘003 mm. 
Thickness of sclerotic in front = 0‘02 mm. 
Thickness of sclerotic at posterior end of pigment = 0'006 mm. 
Thickness of pigment-la 3 mr = 0‘004 to O'Ol mm. 
Diameter (long) of ganglion-cell = O'Ol 2 to 0'02 mm. 
Diameter of nucleus of ganglion-cell = 0 '006 mm. 
Diameter of pigment-granule = 0 '5 mm. 
Family Alciopida:. 
British zoologists have few opportunities of becoming acquainted with these forms, 
which, moreover, . are so delicate, that unless very great care is taken in collecting, the 
spirit-preparations are unsatisfactory. Those in the present collection are unfortunately 
in an imperfect state and much softened. 
The genus was established by Audouin and Milne-Edwards ^ in 1833 for a 
species [Alciopa reynaudii) about an inch and a half long, procured by Eeynaud some- 
where in the Atlantic during the voyage of the “ Chevrette.” They supposed that the 
dorsal and ventral pigment-glands (segmental organs) were branchial in function. 
Their figure in outline resembles Greeffia {Nauphanta). Delle Chiaje^ next ( 1842 ) gave 
three somewhat indefinite figures of two species from the shores of Sicily, viz., Najades 
cantrainii and Alciopa Candida. Krohn^ then ( 1845 ) described the latter and Milne- 
Edwards’ form, and added a new species {Alciopa lepidota), also from Sicily. De 
Quatrefages,^ in 1850 , gave some interesting observations on Alciope Candida (which he 
called Torrea vitrea) and its eyes. The same form was subsequently ( 1862 ) described 
by A. Gr. Costa ° under the name of Liocapa vertehralis, and Delle Chiaje’s other species 
{Najades cantrainii), under the title of Liocapa vitrea.^ He further constituted a new 
genus, Rhynchonerella.'^ Hering, in addition to the foregoing, described in his inaugural 
dissertation three new species from Messina. A young form was discovered by R. Leuckart 
in one of the Firolidse at Villafranca in 1855 , and Claparede and Panceri probably found 
the same species in Cydippe in the Gulf of Naples. • 
In the voyage of the frigate “Eugenie” Kinberg® describes five new species, viz. , 
Kronia angelini (China), Kronia aurorcB (St. Helena), Alciopa atlantica and Alciopa 
1 Annel, p. 214, pi. v. figs. 6-11. ^ Descriz. e notom., &c., Tav. 155, figs. 14, 18, and 21. 
2 Archivf. Naturgescli., Bd. xi., 1845, p. 141, Taf. vi., and Bd. xiii., 1846, p. 36. 
Ann. d. Sci. Nat., ser, 3, t. xiii., 1850, p. 34, pi. ii. figs. 16, 17. 
® Annuario del Museo, &c., i., ii., and iv. 
® Op. cit., ii. A full bibliography is to be found in R. Greeff’s excellent paper. 
^ Op. cit., ii. ® Oversigt o. d. K. I). Vid. SelsJ:. Forhanil., 1861, No. 4, p. 243. 
