ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 625 



brancliiata, and vou Ibering was wrong in denying fhis. The incom- 

 pletely known Notarchus has a small shell very like that of Gastro- 

 pieron mecJcelii, its digestive tract and generative organs are almost 

 exactly like those of Aphjsia, and the same is true of its nervous 

 system. 



In JJmhrella mediterranea the nervous system, as in almost all 

 Tectibranchs, has a very delicate suboesophageal intercerebral commis- 

 sure ; the presence of otocysts was determined, and these orf^ans, 

 though lying in the pedal ganglia, are attached by very small nerves 

 to the cerebral ganglion. The oesophageal nerve-collar of Tylodina, 

 though very like that of JJmhrella, has three instead of two visceral 

 ganglia, and the median one gives rise to the genital nerves. Leach's 

 name of Ascanius is ai^plied to Pleurobranchus memhranaceus and 

 P. tuberculatus, and the genus is regarded as being intermediate 

 between Plenrohranclms and Pleurobranchea. 



Classification of the Lamellibranchs.* — Dr. M. Neumayr gives 

 a new classification of the Lamellibranchs, founded upon the hinge. 



The oldest forms have no, or only the faintest, trace of hin "re- 

 teeth, the shells are thin, and there is usually neither mark of muscle 

 nor of pallial sinus. For these forms, supposed to have two equal 

 adductor muscles and an entire mantle-line, the order Palfeconchfe is 

 proposed. From these are supposed to diverge the Desmodonta, with- 

 out hinge-teeth, or with irregular hinge-teeth, with two equal adductor 

 muscles and with a pallial sinus ; and the Taxodontae, with numerous 

 undifferentiated teeth and two equal muscles. To the first of these 

 groups belong the Pholadomyidje, Corbulidfe, Myidfe, Anatinidse, 

 Mactridse, Paphidse, Glycimoeridae, and Solenid^ (?), and to the second 

 the Arcidse and Nucalidfe. The Tubicol« form a suborder of the Des- 

 modonta. From the Taxodonta branch off in one direction the Hetero- 

 donta, with distinct cardinal and lateral teeth fitting into each other 

 and two muscle impressions (Najadfe, Carinidae, Astartid^e, Crassatel- 

 lidae, Megalodontidae, Chamidae, (Rudistes) (Tridacnidae), Erycinidfe 

 LucinidaB, Cardiidas, Cyrenidae, Cyprinidae, Veneridae, Gnathodontidae' 

 Tellinidae, Donacida?, and in another, the Anisomyaria, with irregular 

 or no hinge - teeth, two unequal muscles or one only, and no 

 pallial sinus. These form two suborders, Heteromyaria (Aviculidte 

 Mytilida), Prasinidae, Pinnidae) and Monomyaria (Pectinidas, Mytilidse' 

 Spondylida3, Anomidae, Ostreidae). The Trigonidae are considered a 

 suborder of Heterodonta, 



Development of Cyclas cornea. f— Dr. H. E. Zieglcr finds that the 

 segmentation of the egg of Cyclas is, from the first, unequal ; and the 

 small cells, as usual, divide more rapidly than the larger. The ewrr 

 like those of the Najadae, has a micropyle ; the earlier stages of cleav- 

 age are passed through in the brood-sacs. The observations on the 

 gastrulation wore incomplete, but there was seen to be invagination, 

 and two largo primitive moscnchym-cells were detected. The differ- 

 ences in the quantity of fluid found between the ectoderm and endo- 



• KB. K. Akarl. WiHH. Wif-n, Ixxxviii. (1884) pp. .^85-420 (1 pi.). Amer. 

 Natural., xix. (188.')) pp. 404-.5. Soe also this .Journal, ante, p. 22f< 

 t Zf;itsfhr. f. WisH. Zool., xli. (I88,'>) pp. r,25-r,0 (2 pis.). 



