Puzzle

 ACROSS

  1 Geographical reference book

  6 Subject where you may be graded on a curve?

 10 E'en so

 13 Fuss in front of a mirror

 14 Salk vaccine target

 15 Cut with an ax

 16 *Pretends (see letters 6 to 9)

 18 Traveler's stop

 19 The Holy ___

 20 Postmortem bio

 21 React to a cringeworthy comment

 23 *"Good question!" (2 to 5)

 26 Cuts with scissors

 29 "Extreme" prefix

 30 Glaswegian girl

 31 Umami, for example

 33 Understood

 36 www.harvard.___

 37 *Multiarmed ocean critter (3 to 6)

 39 Beach ball filler

 40 "That ___ a close one!"

 41 Euphonium relatives

 42 Submit to the IRS

 43 Gem in an oyster

 45 Detect

 46 *Faces off (8 to 11)

 51 Prince William, to Archie

 52 Has regrets about

 53 Pitcher's stat

 56 Allow

 57 Junkyard warning, and a hint to the starred answers' hidden category members

 61 Faux ___

 62 Amino and acetic

 63 Garnish on a toothpick

 64 ___-pitch softball

 65 Mechanical learning

 66 Post-it messages



DOWN

  1 Google Play buys

  2 ___-or-false quiz

  3 Low-cal

  4 Breakfast hrs.

  5 Sewing kit items

  6 ___ Python

  7 In the manner of

  8 What the odd letters in "twitch" spell

  9 Serious trouble, so to speak

 10 "Not a good idea!"

 11 Ergo

 12 Possessed

 14 Picked up the tab

 17 Org. of Magic and Mavericks

 22 Tel Aviv's land: Abbr.

 23 Directions device

 24 Ejects from office

 25 Sephora rival

 26 Boatload

 27 Zilch

 28 "Seems likely"

 31 Set aside

 32 Words in many similes

 34 Sesame and sunflower

 35 Peach or plum

 37 Attorneys' association

 38 Currency in Cologne

 42 Start of a giant's chant

 44 Certain immigrant's subj.

 45 "Leaving already?"

 46 Swallows hard

 47 "Paper Moon" Oscar winner Tatum

 48 Baseball or baseball card transaction

 49 Yours and mine

 50 Rock concert souvenir

 53 Tweak, as crossword clues

 54 Wander around

 55 Years and years

 58 ___-friendly

 59 Joke writer's forte

 60 Progressive woman?

Solution