letters to nature NATURE | VOL 399 | 10 JUNE 1999 | www.nature.com 579 between 270 and 4,000 ms after target onset) and to ignore changes in the distractor. Failure to respond within a reaction-time window, responding to a change in the distractor or deviating the gaze (monitored with a scleral search coil) by more than 1Њ from the fixation point caused the trial to be aborted without reward. The change in the target and distractors was selected so as to be challenging for the animal. In experiments 1 and 2 the animal correctly completed, on average, 79% of the trials, broke fixation in 11%, might have responded to the distractor stimulus in 6% and responded too early or not at all in 5% of the trials. In Experiment 3 the corresponding values are 78, 13%, 8% and 2%. In none of the three experiments was there a difference between the performances for the two possible targets. Differences between average eye positions during trials where one or the other stimulus was the target were very small, with only an average shift of 0.02Њ in the direction of the shift of position between the stimuli. Only correctly completed trials were considered. Firing rates were determined by computing the average neuronal response across trials for 1,000 ms starting 200 ms after the beginning of the target stimulus movement. Tuning curves. Tuning curves were derived by fitting the responses to the 12 directions presented with gaussian functions: r null þ dirGain ϫ exp ð Ϫ 0:5‫ء‬ðdir Ϫ prefdirÞ 2 =width 2 Þ . The four parameters of a gaussian curve capture the four features of a direction-selective cell: preferred direction ( prefdir), response to the anti-preferred direction (r null ), the directional gain (dirGain; the maximal response modulation) and the selectivity or tuning width (width; the range of directions the neuron responds to).

A systematic checklist of the butterflies of Melanesia, Micronesia and Polynesia is presented. A significant number of previously unpublished island records were found in major museum collections in the UK, Australia and the USA. Aspects of butterfly distribution, authorship of names, and taxonomy are addressed, and sources for about 2,200 published butterfly names are incorporated in a comprehensive bibliography of Pacific butterflies. Combined with recent publications dealing with specific areas, such as Papua New Guinea, a working systematic checklist of Pacific Region butterflies is available for the first time.

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Since BCS Warren’s seminal Monograph of the circumpolar satyrine butterfly genus Erebia Dalman, 1816, was published in 1936, more than 320 new names and some 200 papers dealing wholly or in large part with the genus have been published. A modern checklist of more than 1,300 names proposed for butterflies of the genus Erebia (sensu stricto), all of which have been checked at source, is presented together with the source publication and type locality (TL). Also presented is a bibliography of 1,200 published items concerning the genus. The checklist covers the period 1758–2006; such names proposed and papers published as have been noted after the 31st of December 2006 are also included.

Following the authors’ previously published research on Cape Verde butterflies based on fieldwork conducted in 2013, this paper presents additional data on Cape Verde butterflies as a result of further visits to the islands between 16th June and 17th July 2017, and again from 10th November to 14th December 2017. It reports three new island records (São Nicolau, Santiago and Maio) for Euchrysops osiris (Höpffer, 1855), and one new record (São Nicolau) for Junonia oenone (Linnaeus, 1758), discovered for the first time on the Cape Verde Islands (Santiago) by the authors in 2013. Occurrence of Colias croceus (Geoffroy, 1785) on Sal is discussed and a number of records for the island of Raso in the years 2015-2017 made by the Cambridge University Raso Lark survey team are presented. An updated table of Cape Verde butterflies is also presented, together with an outline map of the islands.