134 Dr. R. Bergh on Phidiana lynceus. 



Margo masticatorius mandibulae rainutissime longitudinaliter pli- 

 catus. Denies radulee uniseriati. Denies pectiniformes, medio emar- 

 ginati. 



Only four species can with certainty be classed under PM- 

 dianttj viz. Ph. inca (d'Orb.), PJi, patagonica^ d'Orb., PJi. uni- 

 Uneataj A. & H., Ph. lynceus^ ^gh., n. sp. Perhaps ^. Al- 

 deriana^ Desh. (Fredol?, ' Le Monde de la Mer/ 1864, p. xi, f. 7) 

 and ^. northumbrica^ Aid. & Hanc, also belong to Phidiana. 

 An anatomical examination oiPh. lynceus ^ ^^-t affords several 

 interesting results, particularly with regard to the organs of 

 vision. The eye was observed in the middle of the external 

 margin of the cerebro-visceral ganglion. Immediately behind 

 the eye, and a little further in, another, smaller, shortly pedun- 

 culate globular body was observed, which proved to be an 

 accessory eye; the diameter was 0*05 to 0*06 millim., the 

 pigment black, the lens small, colourless, with a small yellowish 

 kind of nucleus. Close behind the accessory eye a vesicle, spa- 

 ringly filled with cells and nuclei, with thin walls, was seen to 

 protrude from the surface of the ganglion. This vesicle might 

 be the auricular vesicle ; no other organ that could be so in- 

 terpreted was found. Whilst plurality is a frequent phenome- 

 non amongst Acephala and Tunicata, no instance of the normal 

 occurrence of more than one pair of eyes was hitherto recorded 

 in the class of Gasteropoda. The earlier statements concern- 

 ing the occurrence of such an arrangement in the genus Diplom- 

 matina (Bens.) turned out to be founded on a misconception*. 

 Nor was Clapar^de able to find the black spot which Moquin- 

 Tandon stated he saw in Neritina fluviatilis behind the true 

 eye, and which he described as being like an accessory eyef. 

 Agassiz states, in his ^ Lectures on Comparative Embryology,' 

 1849, p. 86, that on a little Margarita from the roadstead of 

 Boston, he had seen a row of eyes placed at the base of the 

 tentacles of the epipodial fringe. But this statement is not 

 borne out by the results of a careful examination of M. gr'on- 

 landica and M. cinerea. When viewed from beneath, the ten- 

 tacles of the epipodial fringe in M. grordandica^ Ch., are seen 

 to issue each from a small depression, of which the inner mar- 

 gin is almost always swollen in the middle, and contains a 

 varying quantity of black pigment ; sometimes this pigment 

 is disposed in the shape of a ring, and in that case these tu- 

 bercles assume a striking similarity to eyes. These tubercles 

 resembling eyes are of very different shapes, sometimes rather 

 oval ; in some cases the pigment is continued along the lateral 



* Comp. A. Adams in ^A.nn. & Mag. N. Hist.' ser. 2. vi. I860, p. 113, 

 and ibid. xii. 1863, pi. vii. figs. 11, 12. 



t Comp. Claparede in Miiller's ' Archiv,' 1857, p. 139, and Moquin- 

 Tandon in ' Hist. Nat, des mollusq. flur. et terr. de la France,' ii. p. 522. 



