140 Mhcclhinooiia. 



8ogmcntatlon takes plafe liore in the manner stated by Clapande 

 and ]Vrec/nikoff : the smaller spherules of segmentation grow round 

 the larger ones ; and after complete segmentation an embiyo is 

 developed wWihi the ef/r^-memhrane, bearing a eiliary girdle, and in 

 its anterior part two eye-spots. The posterior end shows a delicate 

 coat of cilia. It now rotates in its capsule like the embr\-o of a 

 raoUusk, until its egg-membrane is absorl>ed and it can move more 

 freely in the gelatinous envelope. The animal is still quite opaque, 

 when we observe on each side of it two lanceolate seta;, and a pad 

 whicli projects like a handle at the sides and surrounds the animal ; 

 this is the rudiment of the neck-frill. At the formation of the 

 third pair a subulate seta associates itself with the other actsi, the 

 neck-pad becomes elongated with the animal, and a more distinct 

 separation between the fore and hind body appears. At the extre- 

 mity of the latter we still observe a band of cilia striking down- 

 wards ; and at the cephalic extremity, on which tentacles are now 

 sprouting, we see a small tuft of cilia, which soon falls otf. In other 

 respects I may refer for the further development to Agassiz's de- 

 scription of the process in S. spirUlnm, as any thing I could say 

 would be only an unnecessary repetition of what he has said. — 

 ZeitscJir. fur wiss. Zool. Bd. xxi. p. 394. 



On presumed American Specimens of Pelomcdusa. 

 By Dr. J. E. Gray, F.K.iS. S:c. 



The British Museum lately received, along with a collection of fish 

 in spirits, from Dr. \\'uchcrcr, from Bahia, a very large specimen 

 of Pehmedusa suhrufa, which is a common 8outh-, East-, and 

 West-African species. Is this another instance of an African tor- 

 toise having colonized, like Kinivt/s in 8outh America ? It is 

 considerably larger than any other specimen we have received, but 

 I cannot see that it difi'ers in any other respect. 



Corualia described a species of Pelomedusa, which is entirely an 

 African genns, under the name of Pentonyx americana ; and his 

 description will fit young specimens of this species. He .says that it 

 comes from New York. Can that have been from an introduced 

 Bpeciraen of P. stdirufa brought by the negroes from Africa, as 

 Kini.ri/s is also supposed to have been ? 



Note on Trimerella acuminata. By E. Billings. 



The genus Trimerella was founded by me on two s\)ecic?. {T. i/rand!s 

 and T. acuminata) ; but of the latter I had only the rostral half of 

 the ventral valve of a small specimen. I therefore named it provi- 

 sionally, and stated that it differed " from 2\ i/randis in having the 

 spiral extremity much more pointed, and the longitudinal septa 

 running all the way to the beak." (The septa here alluded to are 

 tlie walls between the tubes nuMitioned below.) "Within the last few 

 days, Mr. T. C. Weston, of our [Survey, discovered several new speci- 



