(tethiide)

pl. [NL., + -idæ.] A family of poly branchiate nudibranchiate gastropods, typified by the Tethys, and characterized by the genus by the absence of a [ τετρά βραχυς, of four shorts, tetrabrach i us (tet-ra-bra'ki-us), n.; pl. tetra brachii (-1). [NL., tetra branch (tet'ra-brangk), a. and n. I. a. Having two pairs of gills, as a cephalopod; be IMG:content-0156.png:[blocks in formation] open upon the ex terior; and the oviducts and sperm ducts are paired, but the left is rudimentary. There are many sheathed circumoral tent a cles, not bearing suckers, two hollow eyes, two ol. -ann Pearly Nautilus ( Nautilus pompilius). C, hood; J, funnel; M , shell-muscle; mx , jaws; p., mantle; or , branch iæ; gu , nidamental gland; r,, position of renal appendages; ann , horny ring; ov , ovary; gal , ovifactory organs, no ducal gland; sph, siphuncle; ch , black part of shell under mantle; kn , proce of the ink-bag, and a cartilaginous skeleton into the funnel. large many-cham bered shell, straight or coiled. The order has included both ammonoid and nautiloid forms, but has also been restricted to the latter. They abounded in former times, as is shown by the immense number and variety of fo ils, but are now nearly extinct, being represented by the pearly nautilus only. See also cut under nautilus. tetrabranchiate (tet-ra-brang'ki-āt), a. and n. [