It has recently been established that the filaments seen in the Las Campanas Redshift Survey (LCRS) are statistically significant at scales as large as 70-80 h^-1 Mpc in the δ = -3° slice and 50-70 h^-1 Mpc in the five other LCRS slices. The ability to produce such filamentary features is an important test of any model for structure formation. We have tested the ΛCDM model with a featureless, scale-invariant primordial power spectrum by quantitatively comparing the filamentarity in simulated LCRS slices with the actual data. The filamentarity in an unbiased ΛCDM model, we find, is less than the LCRS. Introducing a bias b = 1.15, the model is in rough consistency with the data, although in two of the slices the filamentarity falls below the data at a low level of statistical significance. The filamentarity is very sensitive to the bias parameter, and a high value (b = 1.5), which enhances filamentarity at small scales and suppresses it at large scales, is ruled out. A bump in the power spectrum at k ~ 0.05 h Mpc^-1 is found to have no noticeable effect on the filamentarity.