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Proton spin-lattice relaxation measurements in some binary liquid mixtures suggest a method for determining, with the BPP translational model, the relaxation contributions related to the coupling of protons belonging to molecules of different types. These mixed translational contributions can be evaluated when the experimental values of the apparent relaxation time and those corresponding to ideal behaviour are not very different. When the translational relaxation times corresponding to the mixed contributions are shorter than the translational relaxation times related to molecules of the same type, a decrease in the reciprocal mobility occurs which involves interaction phenomena such as molecular associations and structure-breaking processes. The opposite case refers to the existence of rather stable structures.

THE genus Diplectrum Holbrook is composed of several species from the tropical-subtropical coastal areas of the western hemisphere. Dr. Leslie W. Knapp, Supervisor for Vertebrates at the Smithsonian Oceanographic Sorting Center, made many collections along the northwest coast of South America. Among the members of the genus Diplectrum examined from those collections were nine specimens of a distinct and new species. Examination of fish collections at the Scripps Institute of Oceanography and the Los Angeles County Museum revealed 17 additional specimens also considered in this report. All Diplectrum thus far examined (Longley and Hildebrand, 1941; Reinboth, 1967; Bortone, 1971) are synchronously hermaphroditic. The new species is no exception and the gonad of one specimen was examined histologically. All measurements were made with dial calipers to 0.1 mm, except standard length of specimens above 100 mm which was recorded to the nearest millimeter. Measurements and counts were made according to methods of Hubbs and Lagler (1964) with the following emendations: cheek scale rows A was made from the posteroventral angle of the eye downward and posteriorly toward the preopercular angle; cheek scale rows B from the posterior serrated upper arm of the preopercle downward and anteriorly to the distal end of the maxillary (Ginsburg, 1948); gillraker counts (made on the first arch) included all rudiments of gill rakers and tubercles; preopercular spines included all spines on the upper arm, spur and lower arm; preopercular spur spines were counted between the upper and lower outside angles of the preopercular spur; interorbital width was measured as the least fleshy width of the interorbital area; cheek length was from the distal maxillary edge to the nearest 61 border of the upper preopercular arm; maxillary width was measured at the broadest part of the distal maxillary area. Dorsal fin support and vertebral counts were made from radiographs. Method of counting dorsal fin supports followed that of Smith and and Bailey (1961). Vertebral counts were separated as to precaudal and caudal by a plus sign with the last caudal vertebrae counted being the hypural. The gonad (formalin fixed) from a 113 mm SL specimen (USNM 208197) was removed, embedded in parafin, sectioned at 10-15 IA, and stained with hematoxylin and Orange GChromatrope 2R. Abbreviations for the institutions cited are: USNM, U. S. National Museum; CAS, California Academy of Sciences; SIO, Scripps Institute of Oceanography; LACM, Los Angeles County Museum; FMNH, Field Museum of Natural History. All specimens collected by Dr. Knapp carry his field number (LK).