function read_mech,filename,dtype,constlabels

;	Open file and read in the number of species in the const array. This is now necessary because 
;	there is the original 124 species mechanism and the new 119. Species_dim is needed to obtain
;	the correct 'spnum'.
;
;	Also return the (string) labels of all constituents
;	
;	'spnum' is species number (for const variable).
;	
;	'var' is a string for the variable type (e.g., 'kel', 'const')
;	'rec' is the time record (integer). ncdump -h filename will tell you how
;	many records are in the file.
;	'idim, jdim, and kdim' are dimensions of lon, lat, and levels.
;	run @get_combo_spec  to get species number.
;
;	Need separate reading statements because of the different names used for species labels in different
;	output file types. (arghh!)
;
cdfid=ncdf_open(filename)
if dtype eq 'amonthly' then speciesid=ncdf_varid(cdfid,'species_dim')
if dtype eq 'idaily' then speciesid=ncdf_varid(cdfid,'freq1_species')
if dtype eq 'overpass1' then speciesid=ncdf_varid(cdfid,'species_overpass')
if dtype eq 'overpass2' then speciesid=ncdf_varid(cdfid,'species_overpass')
if dtype eq 'column' then speciesid=ncdf_varid(cdfid,'freq3_species')

ncdf_varget,cdfid,speciesid,specdim
specdim=n_elements(specdim)

if dtype eq 'amonthly' then speciesid=ncdf_varid(cdfid,'const_labels')
if dtype eq 'idaily' then speciesid=ncdf_varid(cdfid,'freq1_labels')
if dtype eq 'overpass1' then speciesid=ncdf_varid(cdfid,'overpass_labels')
if dtype eq 'overpass2' then speciesid=ncdf_varid(cdfid,'overpass_labels')
if dtype eq 'column' then speciesid=ncdf_varid(cdfid,'freq3_labels')


ncdf_varget,cdfid,speciesid,constlabels
constlabels=strtrim(constlabels,2)

ncdf_close,cdfid
return, specdim
end