No- if a species is known, a more general invention will not be granted. It is not novel. There is a saying that “what would later infringe, if earlier, anticipates”. Or words to that effect. The square infringe on the rectangle so it also anticipates (makes not novel) the rectangle.
From the MPEP
2131.02 Genus-Species Situations [R-08.2017]
I. A SPECIES WILL ANTICIPATE A CLAIM TO A GENUS
"A generic claim cannot be allowed to an applicant if the prior art discloses a species falling within the claimed genus." The species in that case will anticipate the genus. In re Slayter, 276 F.2d 408, 411, 125 USPQ 345, 347 (CCPA 1960); In re Gosteli, 872 F.2d 1008, 10 USPQ2d 1614 (Fed. Cir. 1989) (Gosteli claimed a genus of 21 specific chemical species of bicyclic thia-aza compounds in Markush claims. The prior art reference applied against the claims disclosed two of the chemical species. The parties agreed that the prior art species would anticipate the claims unless applicant was entitled to his foreign priority date.).