occurred. This explanation does fit the observed isotope effects. Our initial results, therefore, suggest that the great speed of many displacement reactions involving large atom nucleophiles in protic solvents may not be due so much to their polarizability as to their ease of desolvation, and that the leaving group isotope effects provide a probe for distinguishing between the two. These results are also consistent with the operation of a concerted transition state as opposed to an intermediate ion-pair mechanism such as proposed by Sneen and Larsen1 ^2 for other reactants and solvents.If these initial conclusions are substantiated by further experiments and are not found to be unduly complicated by the intervention of specific solvation of substituents,13 specific solvation of the leaving group, or mass effects upon changing the• nucleophile, the kinetic isotope effects of leaving groups may result in one of our more powerful yet subtle probes for transition-state geometry. We propose to explore these possible complications further.

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SynopsisCleaning activity at specific cleaning stations was monitored over a depth range of 15-45 m at Salt River Submarine Canyon, St. Croix using the HYDROLAB underwater habitat. We observed over 4600 cleaning events involving 32 host species. Cleaners included the fishes Gobiosoma evelynae (cleaning goby), juvenile Bodianus rufus (Spanish hogfish) and juvenile Thalassoma bifasciatum (bluehead wrasse) and the shrimp Periclimenespedersoni, often active simultaneously at the same stations. Although cleaning was observed to depths of 30 m, the greatest density of cleaning fishes occurred at a sharp break in the bottom contour at 15 m. Clepticus parrae was the dominant fish cleaned by fishes (80% of events), and the graysby, Petrometopon cruentatum, was most frequently cleaned by Periclimenes. Cleaning was initiated by Gobiosoma at 0600 to 0630 h and continued throughout the day as intense bouts of cleaning activity were interspersed with periods of relative calm. Bodianus patrolled areas of several meters and would sometimes rise over a meter above the substrate to initiate cleaning. In contrast, gobies were much more restricted in both lateral and vertical movements. Gobiosoma and Bodianus cleaned 3104 and 1346 hosts during the study compared to only 207 for Thalassoma. This study of a deeper reef area shows significantly more cleaning activity by Bodianus and much less by Thalassoma than has been reported from other studies in shallower water.

To increase our understanding of how large numbers of similar species of reef fishes coexist, we have determined the components of feeding—niche separation among the members of a feeding guild of coral reef fishes. The seven West Indian species of shallow—water squirrelfishes (Holocentridae) comprised >99% of the nocturnally active, benthic—crustacean—feeding fishes at five sites off St. Croix, Virgin Islands. Resources utilization frequencies were determined for food and foraging habitat. Food was partitioned by taxon between the four species that consumed predominantly shrimps and the three species that ate mainly crabs. Food was secondarily partitioned by body size of prey items, particularly in the principal food category. Differences in foraging microhabitat (position within a reef zone) were as important as food differences in separating species. In all cases but one, overall feeding niche overlap was °.25 or less, with a mean value of .13. This low value contradicts statements that reef fishes are generalists with broadly overlapping resource utilization and, compared with overlap values in other guilds, suggests that the mechanism permitting great local diversity within coral reef fish guilds are not basically different from those operating in other ecosystems. The mean overlap in food among the 6 commonest species was significantly different from the mean overlaps of 50 randomly generated competition—free communities (Sale 1974), suggesting that interspecific competition has played a role in the evolution of this assemblage.

from l-bromo-3-pentyne,2 on interaction with methacrolein, gave the allylic alcohol 2 which (without purification) was converted, by the ortho acetate Claisen reaction,3 into the enyne ester 3 in 55% overall yield after distillation4 at 90°( 0.025 mm) (Anal. Found: C, 75.2; H, 9.8). The nmr spectrum6 included a singlet (10) W.