ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 605 



inhabit these shells have not been detected, and the resemblance 

 between the shells of the upper and those of the lowermost zone are so 

 close that no conchologist is to be blamed for associating them with 

 one another. On closer examination, however, of the internal struc- 

 ture, very important differences are to be detected, and the whole 

 account is so instructive that we give a resume of the author's table 

 of differences. 



The three forms may be distinguished as M. glabella, Pseudo- 

 marginella leptopus, and P. platypus. In all cases the shell is that 

 of M. glabella, but while the foot of the form properly so called 

 is broad, flat, and tapers posteriorly, being red in colour, that 

 of P. leptopus is narrow and high, of the same breadth throughout, 

 and colourless, save for black spots at the sides, and that of P. platypus 

 is broad, flat, the same breadth throughout, and colourless. So, again, 

 the operculum is either absent, or is like that of Fusus (unguiculate), 

 or is lamellar, as in Purpura. The tentacles of Marginella are long, 

 the radula has only the middle plates, and these are broad and pro- 

 vided with a number of small teeth, while the pedal gland is large in 

 proportion to the foot. In both Pseudomarginellids the foot-gland is 

 very small ; in P. leptopus the tentacles are short and broad, while in 

 P. platypus they are short and round. The lateral plates of the radula 

 are, in the former, broader than the median plate, but in the latter they 

 are unciform and much smaller. Indeed, P. leptopus appears to belong 

 to the Buccinacea, while P. platypus is probably one of the Purpuracea. 



It is pointed out that, thanks to the investigations of Semper, we 

 know that the very opposite of the conditions here described may in 

 some cases be found to obtain ; that is to say, there are forms (Chlorcea 

 and Dorcasid) in which, though the animals are closely allied, the 

 shells themselves are very different. The studies of later years show 

 that shells with a large wide orifice are very variable ; and now we find 

 that Marginella is a form with a narrow orifice. The author insists 

 on the important bearing which observations of this kind have on the 

 determinations of palaeontologists and the theories of stratigraphical 

 geologists. 



Vascular System of Naiades and Mytilidae.* — Dr. H. Griesbach 

 gives a preliminary notice of his studies on this subject, which has 

 always attracted much attention, in association with the taking of 

 water into the body of these molluscs. The animals were placed in 

 water coloured by green iodide ; and the coloration was sooner or 

 later noticeable in the foot, whence it extended into the most various 

 regions of the body. Jwing to the chemical changes which take place 

 in Anodon, owing to the presence in its tissues of a large quantity of 

 calcareous salts, the tissues will be found to be coloured violet. The 

 author has been able to force injections through the slit-like orifice in 

 the foot (one of which lies quite anteriorly, and the other two at about 

 the middle). The colouring matter may be observed to pass not only 

 into the larger trunks, but also, with care and patience, may be 

 detected in the vessels of the muscles of the foot. 



* Biol. Centralbl., ii. (1882) pp. 305-9. 

 Ser. 2.— Vol. II. 2 T 



