Miftcclfaneous. l,\[) 



base rather more produced. The lower jinv Ims the three deciduous 

 grinders und the six cut tiiif^- teeth all well developed, the two iniddh- 

 ones heiiif^ much the loiififest. The eauines are, as in the .smaller 

 hIcuII, Klender and curved : the lower jaw is much more developed, 

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

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

 animal. 



I give these particulars, as I tliink 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 ui)per and 

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

 shown in M. de Blain\-ille'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 likely 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 car, "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 1'. Z. >■>. 1850, p. 78, tab. xvii.). 



Development of Spirorbis nautiloides, Lam. 

 By Dr. K. vox Willimoks-Suhm. 



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

 in very great abundance, especially on Fticus vesicidosus, ■which it 

 frequently covers closely in association with Memhranijiora. Like 

 its allies S. Pagenstecheri, Quatref., and S. sjnriUum, Gould, it is au 

 hermaphrodite, the yeUowish-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 Pagensteeher* as occurring 

 in a Mediterranean species, does not take place in ^'. 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. fiii- wiss. Zool. Bd. xii. p. 486, pis. 38 & 39 ; I. e. p. 318, pi. 7. 



10* 



