202 ANTROBRANCHIA. 
ORDER V. ANTROBRANCHIA. 
Cyclostoma Lamarck, Cuvier, &e. 
Branchie reticulate, non elevate, ad cavitatem sacciformem 
adhzerentes. Corpus spirale. Testa spiralis. Operculum tes- 
taceum. Os rostriforme. TYTentacula duo, ad basin externé 
dilatata, oculigera. Sexus distinctus, oviparus. 
The branchie are reticulated, not elevated, adhering to a 
sack-shaped cavity. The body spiral; the shell spiral; the 
operculum testaceous; the mouth rostriform ; tentacles two ; 
the base externally dilated, bearing the eyes. The sexes di- 
stinct, oviparous. 
This Order contains several genera, which have been arranged 
together under the general denomination of Cyclostoma. One 
genus only occurs in Great Britain, which contains three Euro- 
pean species. All the genera inhabit dry sandy situations ; the 
greater number living in tropical countries. 
Genus 93. CycLOSTOMA. 
Cyclostoma Lamarck, Cuvier, &c. 
Turbo ductorum. 
Testa spiralis, apice obtusiuscula. dpertura arcularis, li- 
bera, ad dextram acuminata. Peritrema nullum. Umbilicus 
centralis, perforatus. Operculum testaceum, spirale. Sutura 
profunda. 
Animal: os rostriforme. Rostrum annulatum. Tentacula 
cylindrica, ad basin externé abrupté dilatata, oculigera. Oculi 
prominuli, 
Shell spiral, its apex rather obtuse. Aperture circular and 
free, acuminated at the right side. Peritreme none. Umbili- 
cus central, perforate. Operculum shelly, spiral. Suture deep. 
Animal. Mouth rostriform. Rostrum annulated. Tenta- 
cles cylindric, externally at their base abruptly dilated, bearmg 
the eyes. Eyes prominent. 
