Rhomboid
In a rhomboid, the number of across clues is the same as the length of each word. The rhomboid is inherently double (see double forms).
LEFT RHOMBOID
QUARTER
TROUGHS
SANGOUT
DENMARK
ROBBINS
GULLEYS
SELENIC
RIGHT RHOMBOID
RAWWOOL
THREERS
BROMINE
SEAMIST
SCRIBES
PHALLUS
COYNESS