ADDISONIA. 139 



Soft parts : head provided with two tentacles without eyes or eye 

 tubercles ; muzzle plain, simple ; foot thin, orbicular, without lateral 

 or posterior tubercles, processes or fringes ; mantle edge simple, thick- 

 ened ; gill composed leaflets as in Patella, the series starting on the 

 right behind the head and continued within the mantle edge back- 

 ward, the body of the animal being asymmetrically placed with 

 regard to the aperture of the sheU to afford room for the enormous 

 series of branchial leaflets ; anus opening behind and above the 

 head slightly to the right of the median line, and indicated by a 

 small papilla. (Dall.) 



A. LATERALIS, Requien. PL 25, figs. 26, 27. 



Shell oval, obliquely conoidal, very smooth, shining, decussated 

 by extremely fine radiating and concentric striae. Nucleus excen- 

 tric, posterior, obliquely recurved, situated below the lateral apex. 

 Aperture oval, margin simple, acute. (Tiberi.) 



Length of largest specimen 17, width 14, alt. 11 mill. ; but usu- 

 ally smaller. 



Mediterranean; North Atlantic, both European and American 

 shores, living in 50-640 fms. ; found dead in a wider range of depth. 



Gadinia lateralis REQ. Coq. de Corse, p. 39, 1848. PETIT, Cat. 

 Moll. pp. 92, 264, 1869. Gadinia excentrica TIBERI Journ. de 

 Conchyl. 1857, p. 37, t. 2, f. 6. WEINKAUFF Conchyl. des Mittelm. 

 ii, p. 177. DALL, Amer. Naturalist, p. 737, 1882. Tylodina excen- 

 trica MONTS. Not. intorn. Conch. Medit. p. 57, 1872. LOCARD, 

 Cat. Moll. Mar. Fr. p. 67, 1886. Addisonia excentros JEFFR. P. 

 Z. S. 1882, p. 673; 1884, p. 148. Addisonia lateralis DAUTZEN- 

 BERG, J. de Conchyl. 1886, p. 205. DALL, Bull. M. C. Z. xviii p. 

 344. A paradoxa DALL, Proc. U. S. Nat.'Mus. 1881, p. 405, Apr. 

 1882. A. lateralis var. paradoxa DALL, Bull. M. C. Z. xviii, p. 344, 

 t. 25, f. 1 a-e. 



Var. PARADOXA Dall. PL 25, figs. 1, 2, 3. 



Shell ovate, thin, whitish ; apex presenting an appearance as if 

 an embryonic tip (perhaps spiral) had fallen and been replaced by 

 a peculiarly blunt ovate apex, which in the young shell is nearly 

 marginal, posterior and to the left of the middle line, but in the 

 adult is considerably within the margin, curved downward and 

 backward and much more asymmetrical ; sculpture of faint grooves 

 radiating from the (smooth) apex and reticulated by the stronger 

 concentric lines of growth, beside which the extremely inflated arch 



