def get_species_seq_count(species_data): 
    """
    Count number of species within the genus, and list the number of sequences for that species. 
    """
    species_seq_count = []
    for species in species_data.keys(): 
        species_seq_count.append((species, len(species_data[species])))
    species_seq_count.sort(reverse=True, key=lambda x:x[1])
    return species_seq_count