228 



HARDWICKE'S SCIENCE-GOSSIP. 



recorded from British strata ; this is Agassiz' 

 G. latidens (fig. 130), from the Middle Eocene of 

 Bracklesham, Another species {G. aduncus) is found 

 in Continental Miocene formations, and the Tertiary 

 strata of North America have yielded some others 

 (C contortus, &c.)- The extinct Hevupristis appears 

 to have been intermediate between Galeoccrdo and 

 Carcharias, if dental characters are safe guides to such 

 conclusions ; no remains of this genus have been dis- 

 covered in British rocks, and only one species 

 {H. serra) is at present known. Fig. 133 will give a 

 good idea of the curious tooth of Heniipristis. It 

 occurs in the Tertiaries of both Europe and America, 

 being found in the Miocene of Malta and Wiirtemberg, 

 and also in the Eocene and Miocene pf the United 

 States. 



The remarkable Selachoidei, commonly known as 

 " Hammerheads," are classed with the Carchariidce, 



also been made to show that the detached vertebrce- 

 are capable of at least generic determination.* 



Although marked differences can be observed 

 between the living forms of each, Lamna and Odon- 

 taspis are scarcely separable palreontologically, and 

 hence it will be necessary here to consider the latter 

 as a sub-genus only of the former. The teeth of both 

 are of the type shown in figs. 129 and 137, with the 

 crown long, slender, and sharp-pointed, with distinct 

 lateral denticles, and with the root deeply cleft, and the 

 radicles much elongated. Lamna proper is generally 

 much compressed and flattened anteriorly, while 

 Odontaspis is nearly cylindrical in section, and. often 

 has a sigmoidal curvature (fig. 129, a). The teeth of the 

 latter kind appear before those of the former, and the 

 earliest hitherto met with in English strata are from 

 the Gault. Z. {Odontaspis) rhaphiodon occurs in the 

 Chalk, and this tooth (fig. 129) is remarkable for the 



Fig. 139- — Lamna 



{Odontaspis). 



Fig. \^i.—Otodus 

 appendiculatns . 



Fig. 133. — Corax 

 pristodontus. 



Fig. 133. — Hemipristis 

 serra. 



Fig. 1-^.— Corax 

 falcatiis. 



Fig. 130. — Galt'O- 

 cerdo latidens. 



Fig. 136. — OxyrJiina 



Maittellii. 



Fig. 135. — Otodus macrotus. 



and appear to be represented in the fossil state by 

 certain detached teeth. Palaeontologists, however, in 

 this instance, find themselves greatly perplexed, for 

 the dentition of these sharks is much less distinctive 

 than the well-marked characters available to zoologists 

 studying living species would lead us to expect. 

 Teeth of SpJiyrna [Zygtinia) prisca occur in the 

 Miocene rocks of Malta, and the Eocenes of South 

 Carolina, and one species is known from the Chalk 

 Marl, near Dresden. 



LAMNID^. 



The majority of the Selachian fossils found in 

 Cretaceous and Tertiary formations are referable to the 

 Lamnidce, and belong to the familiar genera, Lamna, 

 Odontaspis, Otodus, Oxyrhina, and Carcharodon. 

 The teeth of all these, except Odontaspis, are readily 

 distinguished one from another, and attempts have 



curious ornamentation produced by the folds of enamel 

 (gano-dentine) on the back of the crown ; the structure- 

 of the radical portion is so delicate, that specimens 

 are rarely found perfect, and their condition is usually 

 that of the fossil represented in the figure. L. 

 (^Odontaspis) stibulata is a second Cretaceous species, 

 ranging from the Gault to the Chalk, and destitute of 

 surface ornament on either side. The Chalk examples 

 usually assigned to this species are notably smaller 

 than those from the lower horizons. Only one 

 form in the British Cretaceous formations has been 

 referred to LMiima proper (Z. acitviinata, Ag., from 

 the Chalk) ; but this differs so much from the ordinary 

 type of tooth characterising the genus, that there is 

 reason to doubt the correctness of the identification, 

 and evidence is not wanting to suggest its being a 

 variety of Oxyrhina Mantellii. L. clcgatis (fig. 137) 



* C. Hasse, "Das Nati'irliche System der Elasmobranchier " 

 (Jena, Gustav Fischer, 1879-1S83). 



