Is your geometry UV mapped (or can it be)? If so, the UV mapping type option will give you the best distribution of the texture. If not, try the Tri-Planar mapping type. Also, you could tweak the texture in Photoshop to make it seamless, using Filter > Other > Offset + the Clone Stamp tool and Spot Healing brush. Alternately, you could create the tortoise texture using the procedural Spots texture node, which will map it in 3D.
Cheers,
Eric