ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
621 
discusses the question of cleavage, describes the formation of the meso- 
derm, and makes some interesting theoretical considerations based on 
the view that, as the matter stands now, we are compelled to deny the 
morphological significance of the precise method of the origin of the 
middle layer, if we maintain its homology even within the group of 
Mollusca. 
5. Lamellibranchiata. 
Xlnionidse of Arkansas.* — Mr. R. E. Call has made a study of the 
TJnionidse of Arkansas, with incidental reference to their distribution in 
the Mississipi valley. He points out that less is known about the 
Mollusca of this State than of any other one in the Union. He has been 
able to consult a number of original types with the result that he has 
considerably reduced the number of what he regards as good species. 
Not the least interesting fact connected with the study of the Unionidse 
is the one that numerous species have been duplicated by describing 
the forms assumed by the sexes as of specific value. This has occurred 
in a number of instances, and is responsible for a considerable number 
of synonymic names. The author has reduced the number of species to 
59, 52 of which belong to the genus IJnio, three to Margaritana , and four 
to Anodonta. These molluscs are said to abound in the streams of 
Arkansas. Varieties of species may be relatively few, but individuals 
are very abundant. They are to be sought in every conceivable con- 
dition of bottom and other factors of environment. 
Poisonous Mollusc.^ — M. A. T. Rochebrune finds that Spondylus 
americanus emits an odour of sulphuretted hydrogen which is strong 
enough to disgust even a famished creature, so that it is never preyed 
upon for food. M. Rochebrune has isolated the toxic principle, and has 
obtained an olive-green extract with an acrid odour and bitter taste. 
Chemical reactions indicate that in this mollusc there is elaborated a 
product allied to ptomaines and leucomaines, and very similar to mus- 
carine, the toxic product of the mushroom. 
Bryozoa. 
Mediterranean and New Zealand Reteporae.J — Mr. A. W. Waters 
points out that our knowledge of the Mediterranean Beteporse is most 
unsatisfactory, as so many specific names have been given on account of 
slight differences in the nature of the reticulation. The necessity for 
making an entire re-examination of the group was increased upon re- 
ceiving from Prof. Parona a most interesting fenestrate Bryozoan, which 
at the first glance seemed to belong to Betepora , but which is now 
described as Palmicellaria parallelata. The author doubts, however, 
w T hether it should not be made the type of a new genus. The author 
gives an account of the essential characters of the Beteporse, and describe& 
in detail species which have been found in the Mediterranean. The 
conclusion of the paper is occupied with the description of three species- 
from New Zealand, one of which is new. 
* Trans. Acad. Sci. St. Louis, vii. (1895) pp. 1-65 (21 pis.). 
t Rev. Scient., June 1895. See Amer. Natural., xxix. (1895) p. 760. 
X Journ. Linn. Soc. Lond., xxv. (1895) pp. 255-71 (2 pis.). 
