2 FOSSIL REPTILIA OF THE LONDON CLAY, 



developments of the vertebral ribs (pleurapophyses),* and the marginal pieces as the 

 homologues of the sternal ribs (haemapophyses).t 



I must refer the reader to my Memoir, communicated to the Royal Society, for the 

 facts and arguments which have led me to regard these pieces, as dermal ossifications, 

 homologous with those that support the nuchal and dorsal epidermal scutes in the 

 crocodile. Most of the bony pieces of the carapace are, however, directly continuous, 

 and connate, + with the obvious elements of the vertebrae, which have been supposed 

 exclusively to form them by their unusual development ; the median pieces have 

 accordingly been called " vertebral plates," and the medio-lateral pieces " costal 

 plates." I retain the latter name, although with the understanding and conviction 

 that they are essentially or homologically distinct parts from the vertebral ribs or 

 pleurapophyses with which they are connate and more or less blended. But, with 

 regard to the term " vertebral" plate, since the ribs {costa) are as essentially elements 

 of the vertebra as the spinous processes themselves, I have been in the habit, in 

 my Lectures, of indicating the median series by the term " neural plates," which term 

 has the further advantage of removing any ambiguity from the descriptions that might 

 arise from their being mistaken for the superincumbent epidermal shields, which are 

 likewise called "vertebral plates" m some EngHsh works. § The term ''marginal" is 

 retained for the osseous plates forming the periphery of the carapace ; but the median 

 and symmetrical ones, which seem also to begin and end the " neural" series, are 

 specified, the one by the term "nuchal plate," the other by that of " pygal plate." 

 The " neural plates" are numbered as in the classical Monograph of Bojanus.|| 



In the subjoined woodcut of the carapace of the loggerhead turtle {Chelone caouanna) 

 (fig. \),ch is the nuchal plate ; si to si i the neural plates ; ph topis the costal plates ; and 

 mi to mi2 the marginal plates. The carapace is impressed by the superimposed epidermal 

 scutes or shields, which consist of a median series, called " vertebral scutes'" vi to V5 ; 



* Ibid. p. 211. Rathke has recently supported this determination by arguments drawn from the 

 mode of development of the carapace. See ' Annales des Sciences Naturelles,' Mars, 1846 ; and ' Ueber die 

 Entwickelung der Schildkroten,' 4to, 1848, where he says, p. 105 : — " Ausser den Rippen und den horizontal 

 liegenden Tafeln, zu welchen sich die Dornfortsiitze des zweiten und der sechs folgenden Riickenwirbel 

 ausbilden, dienen bei den erwachsenen Schildkroten zur Zusammensetzung des Riickenschildes uoch eine 

 oder mehrere Knochenplatten," viz. the "marginal plates." I have shown how Rathke was deceived by 

 ovei"-estimating the character of connation, in my ' Observations on the Development of the Carapace and 

 Plastron of the Chelonians,' which conduct to a different conclusion to that at which Cuvier and Rathke 

 have arrived. (Philosoph. Transactions, 1849.) 



t Geofl'roy, Annales du Museum, tom. xiv (1809), p. 7- 



X This term is used in the definite sense explained in my work on the ' Archetype of the Vertebrate 

 Skeleton' (8vo, V. Voorst, p. 49), as signifying those essentially different parts which are not physically 

 distinct at any stage of development ; and in contradistinction to the term " confluent," which applies to 

 those united parts which were originally distinct. 



§ See Griffiths's translation of Cuvier, vol. ix, Synopsis of Reptilia, p. 6 — " fifth vertebral plates 

 prominent." 



II Anatome Testudinis Europaeae, fol. 1821, tab. iii and iv. 



