149 



centrai muscular scar, which is more or less marked with regular 

 cross grooves, and they are evidently impressions of the outer surface 

 of the two branches of the gills. 



Onlj^ one of the specimens I have seen show8 any indications of 

 the outer surface of the shell, and iu that it only forins a band about 

 one-fourth of an mch wide on the edge of the outer Up ; it is pale, 

 greyish, and coucentrically striated, likę the surface of the normai 

 specimen of Haliotis albicans. 



This kind of monstrosity was to be expected, as the mantle of the 

 aniraal is slit under the perforations on the shell ; and we have in 

 Scissurella and in several fossil genera the perforations replaced 

 by a more or less continued slit over the mantle ; but I have never 

 before seen an Ear-shell with more thau two holes united into a short 

 slit by the absence of the shelly matter between them ; but when we 

 exaraine the Haliotis albicans, the existence of the more distant ex- 

 terior groove renders it the species in which one should more readily 

 expect such an abnormal formation to occur. 



I have seen two specimens of two species of Haliotis, which ex- 

 hibited just the couverse deformity, that is, beiug without any appear- 

 ance of the series of perforations, the place of the holes being occupied 

 by a continued convex spirai rib, likę the second rib in Padollus. 

 Most probably in this individual the mantle of the animal was without 

 any slit, and hence the malformation, the water being admitted to 

 the gills by the slight notch in front of the ribs, as in some Emar- 

 ginulee or Scuta. 



Dr. Crisp exhibited the brain and a sketch of the head of a mon- 

 oculous Lamb. It vceigbed 4į Ibs., and was born alive at the fuU 

 period of gestation. There was one large eye in the centre of the 

 forehead, and the nostrils were absent. 



The orbit was formed by the os frontis above, by the malar bones 

 on each side, and below by the superior maxillary bone, the lachry- 

 mal, nasal, turbiuated bones and part of the os frontis being absent. 

 The greater part of the interior of the cerebrum veas absent, the cavity 

 being occupied by serous fluid. The thala7ni, corpora striata and 

 corpus callosum were deficient. No olfactory nerves existed. The right 

 optic nerve only was preseut, and this entered the eye in the usual 

 situation ; the other pairs of nerves were in their normai positions, 

 but those to the museles of the eye could not be clearly traced. 



The humours of the eye were apparently natūrai, but the cornea 

 was rather opaque ; the diameter of the organ was 14 lines ; the 

 weight of the humours 40 grs. ; the crystalline lens large and well 

 formed. 



In Vrolik's ' Tabulae ad illustrandum Embryogenesin Hominis et 

 Mammalium,' a case is related and drawings given of a somevvhat 

 similar monstrosity in a lamb. In this instance, also, " the greater part 

 of the cerebrum vras wanting, and no olfactory nerves were present ; 



