60 Dr. E. von J^9#q^s^^^,^i^i^e\(;|(^(?^^6^(?p, fjf ; 



of fresli water to those of the sea wouW* have ;h^cap3,e,^mall€r;,r. 

 but the increase or decrease according to the zones -vvould i^Qjt^^y 

 have changed, or only unessentially. If we advance to the 

 higher steps of classification, the numerical agreement bctwee^[| 

 the two media constantly becomes greater, but the difFereuce^{j 

 which still remain are of a more essential nature. This is th^q 

 case even in the consideration of the orders : — Of the fourteei^yj 

 which J. Miiller has adopted for the class of Fishes, only five^j^ 

 and these very poor in species (with 1 — 3 genera, and not man^jr, 

 more species), are limited to one of the two media, — the Sire^'Y- 

 noidei and Ganoidei holostei to fresh water, and the HolocephaJ^.fj 

 (Chimcera), Hyperotreti [Myxine)j and Leptocardii (Amphioxu^\ 

 to the sea*. .^j 



1^. Amongst Dana's larger sections of the Crustacea, one-haLJ^^j 

 (seven) in number are certainly peculiar to the sea : — Anomura^ ;{ 

 Stomapoda, Schizopodaj Aploopoda, Anisopoday Merostoma, Cir- 

 ripedia, but these are all poor in species ; not one is peculiar to 

 the freshwater; and of the three principal sections^ Podophthalma^f.,^ 

 Edriophthalma and Cirripedia, two are common. In the Anne-jN,(( 

 lida, on the contrary, we find not only that the majority of thcif, 

 orders (three to two, according to Grube) are exclusively marine,,,, - 

 but also that these are by far the most developed and most'^d 

 numerous. In the Gasteropoda also, the exclusively marine,;^ 

 orders predominate, and hold the balance against the commoi:^Q 

 and freshwater orders together; thus, according to TroscheFsrii 

 classification, there are five orders, Heteropoda, Cyclobranchiata,,,^ 

 Notobranchiata, Monopleurobranchiata, and Hypobranchiata,,.^, 

 against the two common orders, Ctenobranchiata and Rhipido-^.f{ 

 glossata, together with the entirely non-marine Pulmonata and 

 Pulmonata operculata (Troschel, however, excludes the Hetero- 

 poda) ; in the more recent English systems, especially in Wood- 

 ward-'s, we have the two marine orders, Nucleobranchiata and"^ 

 Opisthobranchiata, against the common Prosobranchiata and)<> 

 the non-marine Pulmonifera, but still of the two most numerous '^ 

 orders, the one always includes the common, and the other the ^ 

 non-marine forms (disregarding the Auriculce, Onchidice and Am-"" 

 phihola, which dwell upon the borders). An essential difi'erence 

 for the orders, according to the zones only, occurs with the )« 

 Pishes, the two exclusively belonging to the freshwater {Sirenoidei, '^ 

 Ganoidei holostei), being those which are wanting in the colder 

 regions ; amongst the Gasteropoda the colder zones are destitute 

 both of the marine Heteropoda (Nucleobranchiata) and of the 

 non-marine Operculated Pulmonata, and amongst the Crustacea 



* The Berlin Museum has received an Amphioxus from Ceylon, from , 

 M. Nietner. It is unfortunately not well preserved. 



