364 MANUAL OF THE MOLLUSC A. 



varieties. (Gaskoin.) Six other species are included iu Menke's Australian 

 Catalogue, but require verification. 



The followiug genera, nine of which are naked molluscs, are supposed to 

 be now peculiar to the Mediterranean ; the small number of species show they 

 are aberrant or expiring forms. Cassidaria, Terebratida, and Thecidium are 

 ancient, widely-distributed genera, and the Mediterranean Thecidium occurs 

 fossil in Brittany and the Canaries. 



Histioteutliis, 2 sp. Loljiger, 1. Pediculana, ]. 



Verania, 1. Pleurobranchsea, \. Terebratula, 1. 



Gastropteron, 1. Tethys, 1. Morrisia, 2. 



Doridium, 1. Tiedemannia, 1. Thecidium, 1. 



Icarus,!. Cassidaria, 4 ? Scaccbia, 2. 



The genera Fasciolaria, Siliquaria, Tijloduia. Notarchus, Verilcordia ? 

 Clavagella, and Crania, occur only in this portion of the Lusitanian province. 

 Amongst the peculiar species are: — 



Nassa semistriata. Argiope cuneata. Artemis lupinus. 



Fusus crispus. Clavigella angulata. Trigoua nilidula. 



Tylodina Rafinesquii Spoudylus Gussonii. Luciuopsis decussata. 

 Crania rostrata. Astarte bipartita. 



^gean Sea. Prof. E. Forbes obtained 450 species of mollusca in the 

 .Egean, belonging to the following orders : — 



Cephalopoda 4 Nudibranches I'j Brachiopoda 8 



Pteropoda 8 Opisthobranches . . 2S Lamellibrauches 143 



Nucleobranches 7 Prosobranches 217 Tunicata 22 



Of these 71 were new species, but several have since been found in the 

 Atlantic, and even in Scotland.* The only marine air-breather met with was 

 Auricula myosotis. 



Blade Sea. In the northern part a few Aralo-Caspian shells are found, 

 otherwise the Black Sea only differs from the ilediterranean in the paucity 

 of its species; Dr. Middendorif enumerates 68 only. The water is less salt, 

 and there is no tide, but a current flows constantly through the Dardanelles 

 to the Mediterranean.! 



V. Aralo-Caspian Province. 

 The only inland salt-seas that contain peculiar shell -fish are the Aral and 

 Caspian. The shells chiefly consist of a remarkable group of Cockles which 

 burrow in the mud (see fig. 213, p. 291). No explorations have been made 

 with the dredge, but other species, probably still existing in these seas, have 

 been found in the beds of horizontal limestone which form their banks and 

 extend in all directions far over the steppes. This limestone is of brackish- 



* Trans. Brit. Assoc, (for 1843) 1844, p, 130. 

 + A current from the Atlantic sets in perpetually through the Straits of Gibraltar, 

 and there is scarcely any tide ; it only amounts to 1 foot at Naples and the Euripus, 

 2 feet at Messina, and 5 at Venice and the Bay of Tunis. 



