In making a requirement for restriction in an application claiming plural species, the examiner should group together species considered clearly unpatentable over each other.
Where generic claims are allowable, applicant may claim in the same application additional species as provided by 37 CFR 1.141. See MPEP § 806.04. Where an applicant files a divisional application claiming a species previously claimed but nonelected in the parent case pursuant to and consonant with a requirement to restrict a double patenting rejection of the species claim(s) would be prohibited under 35 U.S.C. 121. See MPEP § 821.04(a) for rejoinder of species claims when a generic claim is allowable.
Where, however, claims to a different species, or a species disclosed but not claimed in a parent case as filed and first acted upon by the examiner, are voluntarily presented in a different application having at least one common inventor or a common assignee (i.e., no requirement for election pertaining to said species was made by the Office) there should be close investigation to determine whether a double patenting rejection would be appropriate. See MPEP § 804.01 and § 804.02.