One of the odd variations of shoulder strap design during the Civil War were those with rounded ends. Although they are uncommon, they are not altogether rare as both artifacts and in period images. To date it does not appear that they denoted any particular category of officers and were just a design variation for someone who wanted an insignia that was a little different.
1st Lt. Evan Malbone Johnson, Jr. (1840-1915) 13th N.Y. Militia Co. G 1861 | Unidentified Captain Wearing Rounded End Shoulder Straps |