10. Apical extremity drawn out Genus _Podolampas_ into a tube Apical extremity not drawn out Genus _Blepharocysta_ into a tube 11. Cross-furrow deep, with great Genus _Ceratocorys_ ledge-like walls Cross-furrow wide, no ledge-like Genus _Oxytoxum_ walls * Presence at Woods Hole indicated by asterisk. KEY TO MARINE GENERA OF DINOPHYSIDÆ. Diagnostic characters: The cross-furrow is above the center of the body, and its edges, as well as the left edge of the longitudinal furrow, are usually produced into characteristic ledges; those of the cross-furrow usually form great funnel-like anterior processes, while those of the longitudinal furrow usually form great, lateral, wing-like processes ornamented by ribs and other markings. 1. Without shell; longitudinal Genus *_Amphidinium_ furrow may open & close 2. With shell; longitudinal furrow 3 unchangeable 3. With distinct apical funnel 4 No apical funnel Genus _Phalacroma_ 4. With great wing-like ledge 5 Ledges very small; body long, Genus _Amphisolenia_ needle-like 5. Ledge of longitudinal furrow 6 extends to posterior end Ledge of longitudinal furrow Genus _Dinophysis_ does not extend to posterior end (Recorded by Peck ('93-'95) as very abundant at Woods Hole and in Buzzards Bay.) 6. Ledge is continued dorsally to Genus _Ornithocercus_ the cross-furrow Ledge is not continued dorsally 7 7. With deep dorsal cavity; Genus _Citharistes_ secondary funnel not notched No dorsal cavity; secondary Genus _Histioneis_ funnel deeply notched * Presence at Woods Hole indicated by asterisk. Genus EXUVIÆLLA Cienkowsky '82. (Klebs '81; Pouchet '83, '86.) The form varies from globular to ovoid, with occasionally a sharp posterior end. Shells are usually somewhat compressed, and consist of two valves, which frequently slide one over the other in such a manner as to show the structure with great clearness. The right shell may have a distinct indentation in the anterior edge. There are two lateral, discoid, brown chromatophores, each of which possesses a central amylum granule. The nucleus is posterior. Salt water. Exuviælla lima Ehr. Fig. 18. Synonyms _Pyxidicula_ Ehr.; _Cryptomonas_ Ehr.; _Prorocentrum lima_ Kent; _Amphidinium_ Pouchet. The shell is ovate, rounded and swollen posteriorly. The anterior border of both shells is slightly indented. The shell is quite thick. The animal moves through the water very slowly. Dark brown in color. Length 48µ; width 44µ. [Illustration: Fig. 18.--_Exuviælla lima_.] Exuviaella marina Cienkowsky. Fig. 19.