Miseellaneous. 139 



base rather more produced. - The lower jaw has the three deciduous 

 grinders and the six cutting-teeth all well developed, the two middle 

 ones being much the longest. The canines are, as in the smaller 

 skull, slender and curved ; the lower jaw is much more developed, 

 extended in front, and broader and much more expanded below, 

 approximating it more closely to the shape of the jaw of the adult 

 animal. 



I give these particulars, as I think they show the order in which 

 the teeth are developed, more especially as attention has lately been 

 called to this subject. 



It appears probable that having cutting-teeth in the upper and 

 lower jaws is the nonnal condition of the dentition ; but, as is well 

 shown in M. de Blainville's plates in his ' Osteographie,' the upper 

 cutting-teeth vary considerably in form and size, sometimes being 

 broad and transverse, and at others circular, and often falling out 

 entirely ; and this is more lilcely to be the case as the same kind 

 of variation occurs in the cutting-teeth of the lower jaw : some- 

 times it is the middle tooth, sometimes the intermediate, and at 

 others the outer that is the broadest ; and in other specimens aU the 

 teeth are either very small or entirely wanting, especially in the 

 animals which have approached the adult state. The series of jaws 

 in the Museum exhibit the same variations in the size and absence 

 of these teeth. 



The size, form, and hairiness of the ear, which has been supposed 

 a specific character for the Abyssinian specimens, I have no doubt 

 depends on the age of the animal examined, more especially as 

 Wolf's admirable figures of two specimens, said to have been fifteen 

 months old, living in the Gardens, from Natal, represent them as 

 having small oval hairy ears (see P. Z. B. 1850, p. 78, tab. xvii.). 



Development of Spirorbis nautiloides, Lam, 

 By Dr. R. von Willimoes-Stthm. 



Spirorhls nautiloides occurs in the Bay of Kiel and in the Sound 

 in very great abundance, especially on Fucus vesiculosus, which it 

 frequently covers closely in association with Memhranipora. Like 

 its allies S. Pagenstecheri, Quatref., and S. spirillum, Gould, it is an 

 hermaphrodite, the yellowish-red ova lying in the anterior, and the 

 seminal filaments (which are furnished with a knob) in the posterior 

 part of the body. The process of development of the young within 

 the pedicle of the operculum described by Pagenstecher* as occurring 

 in a Mediterranean species, does not take place in S. spirillum. In 

 this, according to A. Agassiz, the ova, imbedded in gelatinous cords, 

 are deposited in the shell of the parent, and there undergo their 

 development. This is the case also in S. nautiloides, the beautifully 

 coloured ova of which may be found, at the beginning of June, in a 

 biserial gelatinous cord within the calcareous shell with the parent 

 animal. 

 * Zeitschr. fiir wiss. Zool. Bd. xii. p. 486, pis. 38 & 39 ; I. c p. 318, pi. 7. 



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