198 BRITISH PALEOZOIC PHYLLOCARIDA. 



having a greater length of tooth, with very distinct and elevated cusps, may pro- 

 bably have belonged to a species of larger growth. 



For a description of the Gastric Teeth of Ceratiocaris, compared with those 

 of Dtthj/rocaris,see ' Geological Magazine,' dec. 3, vol. v (1888), pp. 145, &c., with 

 ilKistrations. 



NOTES ON DITHYROCARIS. 



1. The more simple forms of Dlthijrocaris, with ovate-obloug and smooth or 

 somewhat granulated valves, supply 53 out of the 144 known British specimens of 

 the genus. These, represented by Nos. 1, 2, and 8 (D. glabra, 46 ; ovalis, 1 ; and 

 granulata, 6) in the table at page vii, should probably be regarded as forming a 

 special group in the genus. 



2. D. Scouleri (No. 5), having doubtful features in some respects (see page 156), 

 had probably a smooth surface, but differs much from the foregoing in form. 



3. D. testudinea (No. 4) has a speciality in its peculiar ornament of oblique and 

 sinuous stride passing all over its test (page 145). This is an abundant form, 

 there being 24 known out of the 144 British specimens of Dithyrocaris. 



4. The reticulate pattern, with modifications, characterises five British species, 

 of which D. insignis (No. 7) presents the greatest number of known specimens 

 (36). The Irish D. Colei (No. 8) is next most plentiful, but with only 11 speci- 

 mens. The reticulation is faint in D. funlcnlata (No. 6), PI. XXII, fig. 6 ; 

 stronger and irregular in D. insignis (No. 7), PI. XXV, figs. 3 and 5, PI. XXX, 

 figs. 3 and 4, and PI. XXXI, fig. 8. In D. Colel (No. 8), in B. tricornis (No. 10), 

 and probably in D. orbicularis (No. 9), the I'eticulation is emphasised by some of 

 its meshes being produced at the angles into short triangular spines, PI. XXII, 

 figs. 4, 5 a, 5 d, 5 e, and PL XXVII, fig. 4 e. 



5. Short cross-lines between longitudinal strife, as in PI. XXXI, figs. 2 and 4d 

 (D. testudinea) ; and an interstitial network, shown in PI. XVIII, fig. 8, is present 

 in the Canadian D. Belli. 



6. Minute punctation, such as is common in crustacean tests, is seen in many 

 specimens, both of the smooth and the reticulate kind. Thus PI. XVIII, figs. 

 1 and 3 (glabra and ovalis) ; PL XX, figs. 2 and 3 (granulata) ; PL XXVIII, figs. 

 3 and 5 c (cast), PL XXIV, figs. 11 b and 12 d, and PL XXXI, figs. 1—3 

 (testudinea) ; PL XXV, figs. 3—5, PL XXVII, fig. 1 c, PL XXX, fig. 3 d, and 

 PL XXXI, figs. 7 b and 8 c (iiisignis) ; and PL XXVII, fig. 2 c (tricornis). 



