1S2 G. F. MATTHEW: ILLUSTRATIONS OF 



have a test ornamented with tubercles, as is the case iu later larval stages of this form, but 

 the surface of the test is simply punctate as in the broad form. 



Stage 3| X 4 mm. (PI. II, fig. 2 e). — When the head-shield has attained this size, it is 

 found to have scattered tubercles on the surface, similar to those v^^hich mark the adult 

 test. The occipital spine and posterior angles of the middle piece of the head-shield, also, 

 begin to stretch out — this change indicating that increased length has been acquired by 

 the pleurœ — and the glabella begins to exhibit the conical form which that part possesses 

 iu the adult trilobite. 



In the later stages, a continuous enlargement of the posterior angles of the head-shield 

 and lengthening of the occipital spine are the changes of form which most attract attention. 



This species can hardly be considered a typical Ptychoparia ; the pleurae are rounded 

 at the ends, the pygidium has only a few segments and there is no proper spine on the 

 movable cheek of the broad form ; but on the other hand, the dorsal furrow is not profound 

 and the glabella is elevated ; it is redeemed from Solenopleura by the characters of the 

 narrow form. 



SOLENOPLEURA, Ang. 



The original description of this genus by Angelin, ' agrees in most respects with that 

 of a group of species which occurs in Div. 1 c and d, and of which individuals are very 

 numerous. The most important difference is the possession of short points at the genal 

 angles ; these points are not prolonged into spines as in the species of Ptychoparia, but 

 .are short and blunt, and are attached beneath the rounded marginal fold at the genal 

 angle, so that in many examples of the movable cheeks they escape observation, and the 

 cheek appears to be rounded at the genal angle : still these species cannot be described as 

 " mutici " according to Angelin's definition, but for other reasons they should be included 

 iu Solenopleura.- There seems the greater reason for this, since Gr. Liunarsson has added 

 two species to the three upon which Angelin founded his genus ; and they do not in all 

 respects conform to the generic definition. S. cristuta for instance, has eyes approximated 

 to the glabella ' and the dorsal furrow is only of moderate depth ; the fixed cheeks are also 

 described as being considerably lower than the glabella. In these respects it approximates 

 to Ptychoparia, etc. The other species of Liunarsson is flat for a Solenopleura and the 

 movable cheeks do not seem to be known. ^ 



' Corpus ovatum, longitudinaliter trilobiim, crusta graniilata vel elevato-punctata tectum. 



Cajiut latum, semicirculare, convexum, undique incrassatomarginatum .sulcoque intramarginali ; an,guli ex- 

 teriores abbreviati, mutici. Prominentia ovata, sulcum apicalem baud attingens, subintegerriraa, vel utrinque 

 ii-loba. Oculi par\i, semilunares, remoti, genarum medium versus siti. Sutura facialis postice ob oculis ad angulum 

 capitis exteriorem, anticeque ad marginem apicalem decurrens. 



Thorax e segmentis circiter xiv ? sulco plurico canaliculatis, apice rotundatis. 



Abdomen parvum, rotundatum, immarginatum, costis lateralibus distinctis ii-iv longitudinaliter sulcatis ; rachis 

 distincta, lateribus scuti angustior. 



' Some Scandinavian authors bave adopted SdenopUura as the spelling of the name of this genus, but I do not 

 know the authority for this change. Through an oversight it appeared in the latter form in these Transactions 

 for 1886 in a paper by the writer on the Cambrian faunas of Cape Breton and Newfoundland. 



^ Om faunan i lagren med Paradoxides Oëlandicus (1877) p. 370, Tail, xv, figs. 5-6. 



* Om fauna med Conocoryphe exsulens (1879) p. 14, Tafl. i, figs. 16-19 and 20. 



